To install Jenny Mod on a Forge server, you’ll need to make sure both the server and client have the mod installed, just like with any other Forge mod. First, download the correct version of Forge that matches the mod, then place the Jenny Mod .jar file into the mods folder on both the server and your client.
If you're not sure where to get the mod safely, https://jenymod.com/ is the official site where you can find the latest version and instructions—it helps avoid sketchy downloads from unofficial sources.