the way I do it is open up lemmy on the browser and you can copy the fediverse link and paste it into mastodon to search for it, but federation is a whole thing so not everyone who sees something from their instance sees everything from every instance depending on who is federated with who, so with mastodon and lemmy it gets a little weird. Ive seen some tools that help pull more content that otherwise your instance wouldnt automatically get itself so that you can see more replies etc but I havent messed around with that