We’re already building Apps through Atlassian Connect since 4 years ago, we’re now studying the possibility of using Forge in our new app development, but we didn’t find anything that mentions that, can Forge work with Jira Service Management?
Welcome to the Atlassian developer community @malhajj, even if you have been lurking around for a while. 
The short answer is JSM doesn’t have Forge support yet and the isn’t yet a timeline to address. You’ll find other Marketplace partners have hit the same thing, and an Atlassian acknowledgement about the gap in this thread:
Thanks man for the prompt update