I don't know which mod it's from, but if you want to find out, I have a library mod (which is normally just a requirement for my other mods) which goes through the registries and saves reference text files of all items, entities (mobs), potions, etc. You can use it to debug and then uninstall it afterwards if you like.
The text files will appear in config/fantasticlib/reference, and will be created/updated when the game finishes starting up. Just open entitites.txt and search it for "scientist". You'll probably find the full entity name (which includes a mod id).
If you just want to find the actual mob in-game instead, you might be able to do so using LagGoggles, but that depends on how much lag the mob is generating. I'm assuming it's generating enough due to the message spam, but I could be wrong. With LagGoggles installed, press "insert" to open the menu for it, then run a profiling test -> World type. When it's done, open the menu again (if you closed it) and look at the results. If you see the mob on the left you can double click it to teleport to it.
Actually, I think LagGoggles might show the full entity name too, though I can't remember for sure atm.
Oh, and don't move around when running a World-type profiling in LagGoggles. It tends to crash the server if you do.