For HPR, its usually kevlar or tubular nylon - thats what most vendors provide, and both tend to used in kits from vendors. But my question was, why are you combining two different materials in the shock chord instead of just using a single, and since you are already using a type thats normally used in the hobby, what does the second one bring? Not saying you shouldn't, just getting you thinking about it.
Knots is a whole big deep whole to dive into.
Especially when you get into knot strength vs reduction in line strength, and then into braiding, sewing, etc.
For stuff I've done with HPR I mainly use two knots
https://www.animatedknots.com/improved-clinch-knot - tie the shock chord to the quick link, eyebolt/u-bolt or swivel.
https://www.animatedknots.com/alpine-butterfly-loop-knot - introduce a loop into the shock chord line for attaching chutes
But if you read through forums, there are lots of thoughts on this subject