This question already has an answer here:
I feel pretty stupid but it's taken me about 15 minutes to find any reference to the app and api key I've created. I started searching through my profile page but couldn't find anything. I also came across this post (rev. 1 when this was posted), which instead lists apps I've logged into using my stack exchange auth, rather than apps I've created. Incidentally it seems a fairly obscure place to put it. Finally this post pointed me to /apps/oauth/. Is there a link to there that I've been missing?