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