How to run data cable in an attic with blown fiberglass insulation
Blown fiberglass is fairly easy to move aside and replace once the work is done. Do your best to fluff and level it, and try to avoid disrupting areas of high slope, as they'll be more difficult to restore. Where you can, simply staple the cable to the roof truss members rather than dropping it in the insulation. The less you compress it the better.

Be sure to wear a simple dust mask to avoid half a day of coughing afterward. There's a lot of atmospheric dust on top of that already irritating material.