How do I solve the knot puzzle?
Find someone who is good at tying knots and ask them for advice.
Hint:
It's Carol (formerly Car'l) at the beach in Shellmound.
The biggest problem I had with this puzzle was telling this person what the knot looks like then relaying the drawn instructions back to F'ther as spoken dialog (he's a verbal learner).
I found this really helpful. It has all the knots and drawings: http://www.appunwrapper.com/2015/05/07/broken-age-act-2-walkthrough-guide-untying-the-knots/