At least on my instance, you can click the three dots under the post to open up some expanded options, then click the star to save the post.

On Jerboa, there should be a little bookmark icon under each post.

Yes of course. In the web app there’s a little star icon you can click and on jebora theres a little badge next to the vote buttons

Yes you click the star to save post and comments and it’s in the more button next to the reply button if you don’t see it.