Take out the question mark, "seriously" may still work.I remember that Aaron Yan once posted a selfie on Instagram and then a fan commented, '哥哥難道是去哪兒上了自拍課? 這自拍技術, 簡直了, 突飛猛進!'
The question 'Seriously?' wouldn't fit there. I think that I might translate it as something like, 'Did you take a selfie-taking master course, Aaron? Your selfie-taking skills — I literally mean it — have improved so much!'