- I don't know why he took Delta to Dallas. Southwestern is cheaper.
- I don't know why she sold her house. (LISTEN)
- He doesn't know when he will be transferred to Hong Kong.
- I don't know why he moved to Vancouver.
- She doesn't know why he was late to class.
- Who did she go to the marketing meeting with?
I don't know who she went with.
- Does she know when they will arrive?
No she doesn't know when they will arrive.
SUBJECT + don't know + (how, who, what, where, when, which) + pronoun + verb