뭔말인지모르겟여 ㅠ
뭔 = 뭐(what)+는(particle)
말 - words, speech
인지 = 이다(to be)+ㄴ지(GRAMMAR POINT)
모르겟여 is a casual/internet spelling of 모르겠어요 = 모르다(to not know)+겠(GRAMMAR, commonly used with the former as 모르겠다 -> 모르겠어요)
ㄴ지 모르겠어요 - don't know something
인지 모르겠어요 - don't know ... is
뭔말인지모르겠어요 - (I) don't know what (that) word is.