From any site, click your profile picture in the top bar (or your name on any post by you) to go to your profile on that site. Just above your bio, click Network Profile. This includes a list of all your questions and answers. If you have only a few pages of them, you can scroll through looking for the title you remember.
Failing that, on any given site you can enter
user:me in the search box along with keywords and find your posts on that site with those keywords. (Searching my own questions & answers over all stack exchange sites asks for
user:me to work cross-site, but it does not at the moment.)
Which to choose depends on how many possible sites you could have posted on, and how many total posts you have.