The easiest route is seeing a sleep doctor or a pulmonologist if you suspect obstructive sleep apnea. There's an online questionnaire called STOP-bang you can fill out which stratifies your risk and severity. Here it is
http://www.stopbang.ca/osa/screening.php
However the definitive test to confirm whether you have this condition is a sleep study exam. You spend the whole night at a sleep lab, plugged into monitors and they observe how you breathe while sleeping..
If you want to avoid that hustle just buy it online and use standard settings, usually 5 for cpap and 10/5 for bipap...