"from" was one of the suggestions for "til." Does "the knives from the cooks" not work?
Be very wary of hints: A word like "til" has lots of meanings, and the hint system is designed to pick the best-matching hint given the sentence and context and put them at the top. Not all of the hints served are correct or make any sense. In this example only "of" would ideally be shown – the rest of the hints applies to the many other sentences where "til" is used in a different context.
Hints can be dangerous! And by the way: We are not in control of what hints are shown. "on" and "from" has to be in the list, because they are used elsewhere. I wish they could be hidden, but the system has its limitations.
"The knives for the cooks" was accepted. But for me this is not the same as "The cooks' knives". Is it something we can distinguish only by the context?
Yes, the Norwegian phrase carries both meanings. You can rephrase it as "kokkenes kniver" to make it clear that we're dealing with possession, but it's not something that tends to cause confusion.