where is the spam or junk folder on the mail app?
might vary or depend on the account..
When you enter the mail app, if it says 'Mailboxes' in the upper left, tap that.
You should now see your mail accounts listed at the bottom..
If you tap on those it should expand into all the available folders such as drafts, sent, junk, trash
Use the Mail app on your iPhone, iPad, or iPod touch - Apple Support