A man standing on top of a building 44.1 m high throws a stone upward with a certain velocity. After 2.0 s, another stone is dropped from the same point. What must be the initial speed of the first stone so that they both reach the ground at the same time?

Since that's your homework assignment and not ours... What do you think the answer is and how did you arrive at it?

Just apply the logic that the first stone should reach the top of the building at the same time when the second stone is about to be dropped.
Show, your solution if still you have problem in understanding.

Just apply the logic that the first stone should reach the top of the building at the same time when the second stone is about to be dropped.

Sorry, that is not correct. When the first stone falls past the top of the building it will have non-zero velocity. If you drop the 2nd stone at that same time with 0 initial velocity it will take a longer period of time to reach the ground than the first stone.

@carissaang: please show us your attempt at using the standard equations of motion to find the time that the 2nd stone is in flight, and from that the time the first stone is in flight, and finally the first stone's initial velocity such that it reaches 0 displacement at that time.