Все слова в скобках нужно поставить в Present Perfect Progressive

has been learning

how long have you been learning Spanish?

he has been repairing

have been watching

how long have you been waiting..

I have been trying

has been teaching

has been selling

haven't been cleaning

has been forgetting

has been sleeping

have been knowing

has been cooking

he has been feeling

how long have you been taking

has been staying