A brokerage generally reports the gross commission on a 1099-NEC — the full amount before the split and the fees it withheld — which makes gross the figure your books have to carry as income.
The damage from netting runs in two directions at once, which is why it is worth being precise about. Income is understated against the figure the brokerage reported, so the two records disagree and the difference has no explanation attached to it. At the same time the split and the fees never appear as costs, so an agent who nets is effectively paying for the brokerage's share twice — once by not receiving it and again by never claiming it. Recorded properly, all three numbers exist: gross as income, each withheld amount as its own expense, and the deposit as what it is, the balance. What any of that means for a return is your CPA's call and depends on how you are set up; our part is making sure the figures they work from are complete and evidenced.