It's an odd term really, Juniper's Knot resembles a lot fencing, though it being much more mental than physical.
It is when a
mastermind concocts a plan where he will riposte his assailant who is often a stalker, lurker. It means to catch the assailant in a knot where they can't go back nor advance, making them trapped.
It's a process that can take days or even weeks to complete,
normally going very slowly as to not alert said stalker.