Hi there, Zack from Online DMV here, just wanted to jump in and help
First off, congrats to your friend, so please let them see this if you have the chance. In Ohio, if you want to apply for a CDL, you’ll need to pass a knowledge test for the type of CDL that you're going for. Remember that there are different types of CDL licenses!
Make sure your friend also brings documents proving your identity, residency, and Social Security number, like a valid driver’s license, utility bill, and Social Security card. For a complete list of what documents you'll need to bring, just ask the Ohio BMV by giving them a call or sending over an email.
After your friend passes all the Ohio BMV's CDL tests, they'll receive a Commercial Learner’s Permit (CLP), which they'll need to hold for at least 14 days before scheduling a behind the wheel skills test on the road. Again, there's a lot here that I've skipped past for brevity's sake, but the Ohio BMV's website ought to have all the exact requirements and fees.
If you need more clarification though, I'd be happy to help