Which exit is the bus from Haneda Airport to Ikebukuro Sun Prince Hotel?

You mean サンシャィティプリンホテル (Prince of Sunshine

The international arrival hall is on the second floor. There are many exits on the opposite side. Go out directly on the left side. There is an elevator down to the first floor, and the bus stop is outside.

There are many buses going in different directions, and there are special buses going to サンシャィティプリンスホテル.

I really can't find it. You can ask at the information desk. The sign is a big red question mark.