Crossword puzzle resolution

The missing letter is supposed to be a "G".

That makes "SUSSING" going down, for the clue "Figuring (out)."

added later Hjem explains:

In the south we suss things out when we want to know what's what.

For the across answer, TIGERSEYE, clued as "Quartz variety."

But my real problem—I misspelled ADNAUSEAM. Google has more pages with the -UM spelling, but that doesn't make it right, hmmm...

The clue for 36 down is "How about it?" (with the quotation marks in the clue). I was satisfied with WHATSUP, but it was supposed to be WHATSAY.