I have a question about KRUG system:
How i set manually the altitude for jamming target?!

KRUG mode of operation under jamming is pretty similar to what the Volhov has with I87V.
When you put it into jamming range tracking "PA" mode, you can set the target range with the range wheel, and the target altitude with the elevation wheel.

Set altitude, and range can be read out from the DHV instrument

Other thing... Why when i set manually the range for jamming target the Long Track screen shows a dot, representing the calculated location of target?! It was like that on real life, when battery commander putted a simulated range for the jamming target, the battalion commander received it and had it shown on it's screen?

Yes. The I87V at the Volhov also creates you a simulated target distance. It is used to determine the moment of missile launch.

Another things: What's the use of this button?

NaiseFail described it nicely.
It was a guarded and sealed switch during peacetime, to avoid accidental betrayal of this capability.