That might be kind of difficult because each post is going to be different depending on instance, so there won't be one universal link to it. What I would do is post a link to the community like this "/c/CommunityName@instance.tld"
Edit: as an example, this community for me is https://monero.town/c/lemmy_support@lemmy.ml which i can shorten to /c/lemmy_support@lemmy.ml
There's unfortunately no instance-agnostic way like how you can send communities with !lemmy@lemmy.ml. something about the post id being different on each instance makes it too difficult for them to figure out, and they believe it's not a high enough priority to think up a solution.
something like !memes@lemmy.ml/281723 isn’t the best, but would at least make things more consistent across instances and could be formatted by apps and the web UI to look nicer
In not exactly sure what you mean by inside an instance. But your post is
Which someone not on Lemmy could use.
Your client probably has a share or copy link option for a post.
Support / questions about Lemmy.