I'm playing single campaign mode. While walking down the building I'm able to kill guard with knife but then can't throw knife at next guard. Get killed each time. Tried every button on keyboard and every button on mouse. Any suggestions?
Usually in order to throw a knife, you must hit the fire button (Right back trigger). If you are trying that and still unable to perform the action, you should try to restart the mission from the chapter select screen, and not from a previous saved game. Sometimes save data can become corrupt resulting in these kinds of issues.
Try that out and let me know how everything works out!