How do I bookmark this for later?
If you're worried about dealing with your #nostr key or keeping it safe engaging with different clients, then check some of your options in a key management
https://thebitcoinmanual.com/articles/nostr-key-management-tools/
Discussion
I only know Snort offering bookmarks, so if you're using that client, just click on the options under the post and select bookmark and it will be under the bookmark section in your profile, can't speak for other clients