1. Is there a shourtcut to zoom to the mouse position, instead of center of the canvas? (e.g. like in SAI)

2. In Sai if you are drawing with a brush a line and then repeating this line and then again and again the color will become more darker and darker (when you press with the same pressure). But in Krita it doesn't changes, it only changes when you are pressing more harder than before. How to fix it?

1. If you use the scroll wheel to zoom, the zoom will be centred on the cursor position.
Or, if you use Ctrl+Space then you can use left-click + drag up/down to zoom in/out ot the cursor position.

2. That sounds like a brush with special characteristics, or a special mode of brush operation that is particular to SAI.
I don't know of any way of doing that in krita.

ahabgreybeard wrote:1. If you use the scroll wheel to zoom, the zoom will be centred on the cursor position.

Do you know, is there any way to reassign scrolling to a keyboard key?

Scrolling (or actually panning the canvas) is already assigned to the Space key. Press it and hold it and you can do left-click + drag around to pan the canvas.
It's also assigned to middle-click-hold (which seems easier to me) and that is a common way of assigning the 'front' stylus button of a graphics stylus to use that for canvas panning.