The two are not usually lumped together like that unless, it is a nylon/spandex blend.(which I've never seen)
Spandex is usually added about 5% to cotton, or i guess polyester.
If so, your ink needs to stretch so you need an additive or an ink that contains the additive already.
Nylon like used in jerseys, shouldn't need anything. The Nylobond type additives are pretty much designed for adhesion to the waterproofed type nylons like umbrellas, some totes, jackets, rip stop tents, etc.
That said, some folks, even someone here, do use it on shiny dazzle type fabrics, though the ink company folks I have talked to for more than 20 years say it should not be necessary.
I've also seen folks use the Nylobond catalyst just as an aid to curing when they are scared of the usual temps, but low temp cure additive is probably the better choice there as well.
What are you looking at?