user11036: I want to copy the whole settings of the composition to the other, all keyframes, transition points, 3d layer etc. In Adobe After Effects

user6685: This is not possible to do in one step, it is only possible to duplicate compositions:

Select the composition (Import Footage Panel)
Press Ctrl+D (or go to Composition > Duplicate Composition)
As (almost) everywhere in AE, hit Enter on the selected composition to rename the duplicate


When you need to copy the properties of a layer:

Select the Layer
Click on the tiny Triangle > left beside the layers name to open up the properties
Select Transform, Effects or Mask
Press Ctrl+C
Switch to the Second Composition
Select the Layer
Set the playhead to the animation start frame (first keyframe)   
Press Ctrl+V to overwrite all properties and insert all copied keyframes

To check the result, press U on the Layer, this will open up all animated properties of the layer. 
Note: Copying the same properties of different layers is also possible by selecting multiple layers, open up the properties simultaneously, and select them by holding down Ctrl or Shift. 

Related: After Effects: Shortcut for showing all transforming properties of a layer

11036: <p>I want to copy the whole settings of the composition to the other, all keyframes, transition points, 3d layer etc. In Adobe After Effects</p>
 6685: <p>This is not possible to do in one step, it is only possible to <strong>duplicate compositions</strong>:</p>

<ul>
<li>Select the composition (<em>Import Footage Panel</em>)</li>
<li>Press <kbd>Ctrl</kbd>+<kbd>D</kbd> (or go to <em>Composition > Duplicate Composition</em>)</li>
<li>As (almost) everywhere in AE, hit <kbd>Enter</kbd> on the selected composition to <em>rename the duplicate</em></li>
</ul>

<hr>

<p>When you need to <strong>copy the properties of a layer</strong>:</p>

<ul>
<li>Select the <em>Layer</em></li>
<li>Click on the tiny Triangle <kbd>></kbd> left beside the layers name to open up the properties</li>
<li>Select <em>Transform, Effects or Mask</em></li>
<li>Press <kbd>Ctrl</kbd>+<kbd>C</kbd></li>
<li>Switch to the <em>Second Composition</em></li>
<li>Select the <em>Layer</em></li>
<li>Set the <em>playhead</em> to the animation <em>start frame</em> (first keyframe)   </li>
<li>Press <kbd>Ctrl</kbd>+<kbd>V</kbd> to <em>overwrite all properties</em> and <em>insert all copied keyframes</em></li>
</ul>

<p>To check the result, press <kbd>U</kbd> on the <em>Layer</em>, this will open up all animated properties of the layer. </p>

<p>Note: Copying the <strong>same properties of different layers</strong> is also possible by <em>selecting multiple layers</em>, <em>open up the properties simultaneously</em>, and select them by <em>holding down</em> <kbd>Ctrl</kbd> or <kbd>Shift</kbd>. </p>

<hr>

<p>Related: <a href="https://video.stackexchange.com/questions/17326/after-effects-shortcut-for-showing-all-transforming-properties-of-a-layer">After Effects: Shortcut for showing all transforming properties of a layer</a></p>
