always found it easy to do myself Borut....but what one should do is stick his/her hand in the freezer for 10 minutes first! Then I have issues.

No, but thanks for the idea.

What other knots, besides the clove hitch, should one know how to do with one hand?

Not on purpose buddy....but yeah..I have "Joe Simpsoned" it a few times...

When I was first learning how to tie all the knots, my testers insisted that I tie the common knots blindfolded. I thought it was totally crazy to expect me to be able to do that.
But you know, even today, some 45 years later, I still can do the most common knots that way, and correctly. There is something about learning the knots to the point where it becomes almost "second nature" and that includes tieing prusik with one hand only. As Dow pointed out, when one is in a bind, tired, wet, frozen to the bone etc., this knowledge will pay off.