The traditional approach is to insulate the kneewall and the attic floor behind the kneewall.
How to insulate a single story attic.
There are two ways to insulate triangular attics behind kneewalls.
Lay the batts across the ceiling joists covering the existing insulation.
While wearing dust mask and gloves carry r 38 batts of unfaced fiberglass insulation into the attic.
Press and tuck the edges of each part of the blanket to make sure they fit snugly and that there are no gaps between.
To build a catwalk you would usually elevate a section of the framing perhaps with 2x6s installed at 90 degrees to the joists and you would install osb or plywood on top of the elevated framing.
This method can be made to work but the necessary air sealing details are demanding and fussy.
Cut a hole in the insulation wherever there is electrical wiring.
A better approach is to insulate the roof slope above the attic.
Pull the wiring up through the hole and rest it on top.