Finding comments on YouTube can be tricky. Especially if they weren't comments made on your own channel, or if you're not signed up for notifications. I don't like being bombarded with push notifications and emails so I have them turned off. I've found two easy ways to quickly find comments on YouTube.
First, you can always go to go to the left column and click History and then click on the Comments tab to see all of your own comments ordered by the date they were made.
Second, you can use the following syntax in a Google search where "John Doe" is the YouTuber's username. You can replace "weeks ago" with "days ago" or "months ago" etc.
I hope this helps - comment on everyone!