Had God ever had to ask Adam where he was before sin?
No. Before sin, Adam and Eve fellowshiped with God every day and were His; there was no separation. Only after sin entered did God ask, 'Where art thou?'—not because He did not know, but to show that sin had separated them from Him and they were lost.
Les explains that redemption is not a Pauline invention; it goes all the way back to the Garden of Eden. God placed Adam and Eve in the Garden, and they were His, fellowshipping with Him every day. But sin came in, and He lost them because He could not fellowship with them in their sin. Les suggests God went out into the Garden—not that He didn't know where they were—to show that they were now so separated from Him. The first question He asked was 'Where art thou?' He never had to ask that before. As soon as sin had separated them and He had lost them, He could ask, 'Where are you?' Adam should have answered, 'We're lost.'