For instance, this one (link to a post to [email protected]): https://reddthat.com/post/20260613
Pasting it in your search bar should give you this kind of results:
You can then click on it to access the post from your instance (in this example, lemmy.zip: https://lemmy.zip/post/16918691)
A community to talk about the Fediverse and all it's related services using ActivityPub (Mastodon, Lemmy, KBin, etc).
If you wanted to get help with moderating your own community then head over to [email protected]!
Learn more at these websites: Join The Fediverse Wiki, Fediverse.info, Wikipedia Page, The Federation Info (Stats), FediDB (Stats), Sub Rehab (Reddit Migration), Search Lemmy
Here is an excellent comment from 3 days ago, so it should be federated everywhere by now? I just shared that link with someone else in fact, in an unrelated reply. I then went to Lemmy.World and searched for that link, but it does not find the original, although it does find my recent sharing of it. I also searched on reddthat.com, and saw the same behavior. And lemm.ee as well. So the "sometimes it works" effect may have some additional not-entirely-characterized triggers for that behavior, but it definitely does not work all the time as a "find this comment" feature as we are discussing.
So as it now stands there is a way to use this search feature to find posts, but not reliably to find comments. Though that is still more than I knew a week ago before Blaze shared this trick with me then:-).