I have a Busnell Sportview scope, 3.5-9X, mounted on a rifle and they were stored for a few years. The magnification ring (knob) is stuck on 3.5X and I can't turn it to increase magnification. I can't turn it using manpower nor pliers. How would one properly get it "unstuck" and would it be safe to put lubricant in there? I do not see any rust.

I'd try longer handled pliers. If that don't work or you do fatal damage to the scope, then buy a better scope.

Nothing you can do will hurt the value of that scope, so spray, pry, or wrench as you wish. If the mounts are any good, do try to salvage them to mount a better scope in. But, the mounts are likely your problem in that a frozen power ring is typically a result of the mounts binding the scope body and the cam which must turn/slide to change the power.

The old 4x fixed power Sportviews were actually pretty serviceable scopes. The problem with cheap scopes comes when the manufacturer attempts to build the variable feature in. The power cam is almost alwasys out-of-round or otherwise off-kilter, causing your point of impact to vary as you change powers. Also, the higher the power, the more distorted the image with the cheap variables.

Thanks for the advices. A better scope is in order.