The DM is well within his rights to say you don't know anything about a monster. If it's a scholar, perhaps he could get a roll at DC 25 with disadvantage if it was a rare desert monster. If, say, the roll was at +7 he'd still have a 2% chance of knowing. Does that seem high or low for a rare desert monster? If he was at +8 he'd haev a 4% chance. Neither of those chances seem particularly out of the ordinary.
As a DM, I often rule that I roll for the player if I don't think he should know how effective he was at doing something. Example, a player rolling a 20 + bonus on Perception can deduce that there really isn't anything to find but if I roll in secret all he knows is that he didn't find anything, not that there wasn't anything to find.
In the case of a scholar, I'd probably take a moment to come up with a DC and a rationale behind it and let the player roll.