We just put an addition onto our family room. The old family room is a concrete slab and the new addition uses Advantech t&g subfloor which everyone tells us is a great subfloor. The contractor did a fantastic job of matching up the level between the old and new floor, but there is an area that falls outside the 3/16" over 10 foot rule, and we'll take care of that. And we'll have to fill in the 1/4" to 3/4" gap between the wood and concrete. My question is, can we nail/staple the 3/8" Bruce engineered flooring over the wood subfloor and glue the material over the concrete? Or should we glue the whole thing?
On the old concrete, we had some tile installed which I removed. But there is some adhesive left over from the tile uncoupling membrane. That all has to be removed, right?

You can leave any old adhesive after the floor has been sanded smooth using 12 or 16 grit. It may start to melt from the abrasion and clog the sandpaper, so get extra.
I staple over plywood next to a glue-down and there had no problems.