Marlin 30-30 cant read model type, no serial numbers anywhere, how do i find out any info? all i know is that it was my grandfathers

There is most likely a serial number on the tang, below the lever. Open it it, there's one somewhere.

Marlin had a few models of .30-30s, but they are all similar. A picture would help. Round bolt or square bolt (the bolt is the part that sticks out the back of the receiver, over the hammer, when you work the lever)? Read off any/all numbers, letters, or any chicken-tracks that you can off of the barrel.

Also, if you can count the grooves in the inside of the barrel, that might help date it.

If all else fails pull the butt stock off and check the side of the top tang, the part that goes into the butt stock.