Minecraft Version: 1.9.4
Inventory Tweaks Version: 1.61-dev53

I struggle to find the server side sorting component. Am i supposed to install the same .jar as for the client? It's not picked up by bukkit/mcmyadmin.

It's the same jar, and is still a Forge mod, not a bukkit plugin.

A bukkit plugin is theoretically possible -- you just need to have a network channel handler that's compatible and does the 'right thing', but I don't have much familiarity with it, and bukkit's legality is still a rather gray area so it's never been a priority.