There is a locked question where I would like to leave a comment ("I think this question would work well at Language Learners Beta; if you repost there, please notify me").
I can't leave a comment and I can't edit the post. Help!
The question on meta doesn't need to be unlocked; you can simply leave your comment on the original question on the main site (which is unlocked).
Update: The question on main has been deleted by its owner, but it looks like you were able to leave that comment before that happened.
When a post is locked due to a rejected migration, the revision history is linked in "migration rejected from english.stackexchange.com N hours ago", which is in the banner underneath the post:
From there, simply click "Return to Question", which should be at the very top of the revisions history (if the question is deleted and you don't have 10k rep, you will not see this):
If you’re in the app, your first step is to get out of it and into a browser. The mobile site works the same way as the full desktop site; the only difference is the appearance of the locked notice, which is very slightly different.