user-1: Do enlightened people "know" what nirvana is like? Obviously, they can't express it to anyone else, so the question isn't super helpful. I just wondered whether nirvana is a thing that we can know as well as experience or taste.
One response, one I don't (personally) want to hear about (at least without some in depth quotation) is that nirvana isn't "like" anything. And, of course, nirvana isn't similar to anything.
I'm asking whether Buddhas of any sort "know" the qualities (e.g. bliss) of nirvana.

user43: Nirvana is an application of the fire-metaphor (a fire going out) used to point at certain aspects of The Goal.
What aspects?

dispassion, disenchantment
the finality (no state subtler than this, nothing further to be attained, no realization that is more fundamental, no fuel to burn, no further becoming)

There are other aspects of The Goal not covered by the metaphor of Nirvana, and to indicate these aspects we use other concepts, namely

liberation
peace
suchness
Enlightenment, Awakening, Knowledge
bliss, happiness
the emptiness
the other shore
the deathless
the unconditional 
one's true nature
the unborn

These describe various other aspects of The Goal (not of Nirvana, which is just one concept among many).
It is therefore incorrect to say that Buddha knows Nirvana or experiences Nirvana. Buddha experiences what Buddha experiences, and he can invent various ways to talk about it, including the metaphors like Nirvana. Buddha knows and experiences The Truth, and Nirvana is only a didactic device used to talk about attainment of Truth and its personal implications.
All these terms and descriptions remain in the conceptual field, as qualities or aspects that try to characterize The Goal by relating it with something the listener knows from his own unenlightened experience.
In one important sense, attainment of Nirvana is a personal transformation. As you change, reality you perceive changes as well, so all these concepts are attempts to describe both the change as well as the new reality, in contrast with old. 

user8157: Ud 8.1 says Nibbana is a sense object (ayatana) therefore it is obviously something known. 
MN 26 says:

Then the thought occurred to me, 'This Dhamma that I have attained is
  deep, hard to see, hard to realize, peaceful, refined, beyond the
  scope of conjecture, subtle, to-be-experienced (vedanīya) by the wise.

SN 56.11 says:

‘This noble truth of the cessation of suffering has been realized (sacchikata).’

Concise Pali English Dictionary sacchikata pp. of sacchikaroti
  realised; experienced for oneself.
PTS Pali English Dictionary sacchikata seen with one’s own eyes,
  realized experienced

The Dhammapada says:

205. Having savored the taste of solitude and peace (of Nibbana), pain-free and stainless he becomes, drinking deep the taste of the
  bliss of the Truth.

Nibbana is the dropping of all burdens; like the experience of relief when urgently urinating or dropping a heavy backpack or drinking cool fresh water on a hot day. 
Read more here: SN 43.14-43 and Nibbana For Everyone

-1: <p>Do enlightened people "know" what nirvana is like? Obviously, they can't express it to anyone else, so the question isn't super helpful. I just wondered whether nirvana is a thing that we can know as well as experience or taste.</p>

<p>One response, one I don't (personally) want to hear about (at least without some in depth quotation) is that nirvana isn't "like" anything. And, of course, nirvana isn't similar to anything.</p>

<p>I'm asking whether Buddhas of any sort "know" the qualities (e.g. bliss) of nirvana.</p>
 43: <p>Nirvana is an application of the fire-metaphor (a fire going out) used to point at certain aspects of The Goal.</p>

<p>What aspects?</p>

<ul>
<li>dispassion, disenchantment</li>
<li>the finality (no state subtler than this, nothing further to be attained, no realization that is more fundamental, no fuel to burn, no further becoming)</li>
</ul>

<p>There are other aspects of The Goal not covered by the metaphor of Nirvana, and to indicate these aspects we use other concepts, namely</p>

<ul>
<li>liberation</li>
<li>peace</li>
<li>suchness</li>
<li>Enlightenment, Awakening, Knowledge</li>
<li>bliss, happiness</li>
<li>the emptiness</li>
<li>the other shore</li>
<li>the deathless</li>
<li>the unconditional </li>
<li>one's true nature</li>
<li>the unborn</li>
</ul>

<p>These describe various other aspects of The Goal (not of Nirvana, which is just one concept among many).</p>

<p>It is therefore incorrect to say that Buddha knows Nirvana or experiences Nirvana. Buddha experiences what Buddha experiences, and he can invent various ways to talk about it, including the metaphors like Nirvana. Buddha knows and experiences The Truth, and Nirvana is only a didactic device used to talk about attainment of Truth and its personal implications.</p>

<p>All these terms and descriptions remain in the conceptual field, as qualities or aspects that try to characterize The Goal by relating it with something the listener knows from his own unenlightened experience.</p>

<p>In one important sense, attainment of Nirvana is a personal transformation. As you change, reality you perceive changes as well, so all these concepts are attempts to describe both the change as well as the new reality, in contrast with old. </p>
 8157: <p>Ud 8.1 says Nibbana is a sense object (<em>ayatana</em>) therefore it is obviously something known. </p>

<p>MN 26 says:</p>

<blockquote>
  <p><em>Then the thought occurred to me, 'This Dhamma that I have attained is
  deep, hard to see, hard to realize, peaceful, refined, beyond the
  scope of conjecture, subtle, to-be-experienced (<a href="https://suttacentral.net/define/vedeti" rel="nofollow noreferrer">vedanīya</a>) by the wise.</em></p>
</blockquote>

<p>SN 56.11 says:</p>

<blockquote>
  <p><em>‘This noble truth of the cessation of suffering has been realized (<a href="https://suttacentral.net/define/sacchikata" rel="nofollow noreferrer">sacchikata</a>).’</em></p>
  
  <hr>
  
  <p>Concise Pali English Dictionary sacchikata pp. of sacchikaroti
  realised; experienced for oneself.</p>
  
  <p>PTS Pali English Dictionary sacchikata seen with one’s own eyes,
  realized experienced</p>
</blockquote>

<p>The Dhammapada says:</p>

<blockquote>
  <p><em>205. Having savored the taste of solitude and peace (of Nibbana), pain-free and stainless he becomes, drinking deep the taste of the
  bliss of the Truth.</em></p>
</blockquote>

<p>Nibbana is the dropping of all burdens; like the experience of relief when urgently urinating or dropping a heavy backpack or drinking cool fresh water on a hot day. </p>

<p>Read more here: <a href="https://suttacentral.net/sn43.14-43/en/bodhi" rel="nofollow noreferrer">SN 43.14-43</a> and <a href="https://www.dhammatalks.net/Articles/Bhikkhu_Buddhadasa_NIBBANA_FOR_EVERYONE.htm" rel="nofollow noreferrer">Nibbana For Everyone</a></p>
