Can a 2 cm staghorn calculus be treated with shock wave lithotripsy? will this procedure decrease or damage my kidney function? my gfr is 60?

It's certainly worth a try. You don't really want to leave that there as kidney damage and/or infections and pain could occur. The other option being surgery. I would give lipotripsy a try, as there is very low risk of the procedure. If it doesn't work, then you can talk with doc about next plan....

stag horn stones can be broken by shock wave but a better procedure is laser lithotripsy thro ureteroscopy or per cut. (approach. from the side) consult a urologist who sub specializes in kidney stones. You should be fine as your GFR is great

2 cm kidney stone is quite large for shockwave lithotripsy and unlikely to break up in sigle session. Laser lithotripsy in hands of expert urologist with expert stone experience is more likely to be definative. PCNL (Per-cutaneous nephro-lithotripsy) performed after temporary placement of cutaneous nephrostomy tube is most definative. Do some research to find your local stone expert urologist.