I'd be very grateful if we could be able to have a one-on-one meeting.
I was wondering if we would/could be able to have a one-on-one meeting.
上司に面談の日時を提案する時は、
"I was wondering if we would/could be able to have a one-on-one meeting."
"I'd be very grateful if we could be able to have a one-on-one meeting."
です。
”I was wondering if ～”/ "I'd be very grateful if ～”
は、相手に対し控えめに依頼する際に使います。
"I'd like to meet on Monday at 2:30pm if you are available."
「もしご都合がよろしければ、月曜日の2時半はいかがでしょうか。」
"Would you mind asking your secretary/assistant to come along with you as an interpreter?"
「秘書の方に通訳として同行していただてもよろしいでしょうか？」
「秘書」は、"secretary"もしくは "assistant"です。
"come along with ~"は、「～に同行する」
ご参考になれば幸いです。
日本 
