I can imagine lots of stuff that doesn't exist (interstellar spaceships with earth as their origin, pink elephants wearing tutus, time machines and so on). But when I limit my imagination to those things that can be constructed using the laws of physics as we currently know them knots without friction drop right off the menu along with the items above.
So if your question was serious then I consider it answered, if you want to seriously know whether something that can't exist can be imagined then the answer is yes, you can imagine it (and so can I), but I can't imagine making one because that would violate the laws of physics somewhere along the line.
You could tie a knot in frictionless rope easily enough, but it would come apart without any work at all and it would not hold anything and you wouldn't be able to grip the rope on either end to tie the knot in the first place. Friction and knots go together unless you're living in a mathematical ideal world, which we don't.
You didn't ask if it's possible to have a knot perform the same tasks (break an uncontrolled descent) without friction, you asked if there were any examples of such a knot.
Is it possible? I can't rule it out.
Are there existing knots that do so? None that are commonly known, no.
