Im trying to use the trademark search in the uspto to find the ownership status of several games that gog could have on their catalog.
Their help guides dont help, they're worthless. Anybody could help with it? Like, do i type the game's title in the Assignor,Assignee, or Applicant section?

All those categories would either be the game's original dev or publisher, not the game title.

Not sure what form you're using but [url=http://tmsearch.uspto.gov/bin/gate.exe?f=searchss&state=4803:4g5ok7.1.1]this one[/url] has a "search term" field and I've successfully found several of Valve's trademarks by entering titles such as Half-Life or DOTA. Anyway, that's not a good approach. Trademarks expire unless renewed and games can change owners which you won't be able to track unless the new owner did renew the trademark which is very unlikely in case of "lost" games.

Theoretically at least 'dead' trademarks do have their information kept- it's actually a lot more effort to cull them than their storage is worth, plus they are legal documents- but you do have to hope it got computerised/ digitised for older entries, as it isn't always the case. Information on contacts, actual ownership and the like may well be out of date, of course.

Something like the basic word search in [url=http://tess2.uspto.gov/bin/gate.exe?f=tess&state=4810:dyakm8.1.1]TESS[/url] (Trademark Electronic Search System) via the USPTO site would probably be easiest as it uses a very simple standard keyword system. Just stick in the game title or a part of it, or developer/ publisher name. The other searches are more specialised and generally not needed unless you want to check something specific.

There's also a copyright search, which many people tend to forget about.

Go to homepage:
http://www.uspto.gov/trademark

Under "Trademark Tools & Links", click on "TESS" which is next to the maginfying glass image.

From there, you can choose "basic word mark search" from the different options.

Then, just type whatever you're looking for in "search term" then hit "submit query" (search "warcraft" for example).

IMPORTANT: not every games is trademarked because it's a different thing than copyrights (and even then, some companies don't bother to register their work at the copyright office)

What games are you wondering about?

I also recommend to check out this thread.

How do i find a games' copyright in that case?

http://cocatalog.loc.gov/cgi-bin/Pwebrecon.cgi?DB=local&PAGE=First