Should I correct a single trivial typo in a submitted manuscript after they rejected the first submission for having too many typos? I sent a paper to a journal and they replied that there were many typos that needed to be corrected. I tried my best to fix these errors, and, after reading the paper numerous times, I resubmitted the paper. Now, however, I found a trivial typo in a comment. My question is : should I wait for their response or tell them about this typo now?
I'm assuming you sent it for another round of review. Wait for their comments. Provided that you really did remove most of the typos in your manuscript, and otherwise followed the reviewers' recommendations, I really doubt this will be an issue.

If, however, you sent the camera ready version to the journal, then you should consider contacting the editor and ask if you could re-submit a corrected version.