WHO + DO

Cuando es sujeto del verbo, who no utiliza auxiliar en preguntas: Who went with you? Who spoke first? Who kicked you in the butt? Who comes here at five o’clock every day? 

Si no es sujeto sí necesita el auxiliar do: Who did you play with? Who does she sleep with? (Aquí you y she son los sujetos del verbo)

Consultar mi GRAMÁTICA INGLESA PARA TORPES, en papel o e-book, de Anaya Multimedia, 2013.