As you must be already aware, Qatar is a Muslim country. Locals most often wear their traditional costumes, but that doesn't imply that you have to wear their traditional suits too. But Qatar appreciates the modest clothing concept. As long as you cover your shoulders, upper arms, and knees, you are okay to enter public places in Qatar. This rule applies to both men and women. Carry a scarf with you wherever you go, so you may use that if any requirement arises.