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"
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