Hello I have this circa. 1990 Tunturi MB that I ride for city and rail trail. I want to put some cheap Suntour or Judy Rock Shocks forks on it (suspension). Can one of you experts tell what kind or size I need to get that will work with my bike. Thanks. See photos.

That'll open up a can of worms. Any sus fork will be considerably taller than your rigid, which will change the geometry and handling of the bike. Some worry about the extra stress on the headtube/downtube joint.
An educated guess is that you need to look for a 1 1/8" threaded fork, unless you want to convert to threadless/aheadset. Make sure the threaded section is long enough to fit the headtube length of the intended frame.
Oh, should be for 26" AKA 559 mm wheels, and have bosses for rim brakes.

I guess maybe I should just forget about it, sounds liek it might be a headache. thanks anyway

I thought a threaded headset meant using a 1" threaded fork.

In any case, old-style mountain bikes with rigid forks can be good commuters with semi-slick or slick tires.

While not as common, there were 1 1/8" threaded forks & headsets, too. I personally couldn't hazard a guess which size the OP's bike would use.

Doesn't have to be. Personally, I've seen more with 1 1/8" than 1".
Hence my guess.
Anything built as a real, adult sized MTB w/ a cassette hub is most likely to be that dimension. But the juveniles, freewheel lookalikes, thats where I'd expect a 1"