I was wondering what do you use to hear knock?
I have original sensor on block (bosch 3 pin)... maybe i could connect it to MIC-in on laptop and use some program to filter "noise".
Would that work or is there better solution?
I think there's been a few discussions on this sort of topic, some have made small amplifiers to listen with head phones, others use laptops with programs like Audacity to provide the filtering. There is a difference between the ideal mic impedance and that of the Bosch sensor though, so you need to consider that.
I have used a Bosch knock sensor connected to the microphone input on the tuning laptop with some success. Recording with Audacity allows adjusting the filter later. I found in-ear headphones with earmuff style hearing protection over top allows you to monitor the knock sensor while tuning. I did this while on the dyno, though, and it may not work very well on the street - I know where I live I am not allowed to use headphones while driving.
add in series 10-100nF condensator to make high pass filter.