To check your Challenge Level, go to Dashboard and you'll see the status bar at top center.
Challenge Level is the level system in the KooBits ProblemSums. It’s based on accumulated Challenge Points (CPs) since the account’s created.
Basically, you're Level 1 as a fresh new user; and you'll be upgraded to next level for every 100 CPs earned till 1000 CPs accumulated; then upgrading to next level for every 500 CPs till 10,000 CPs; lastly every 1000 CPs for upgrading a level.