Who do I have to deliver the pumpkin soup to?

Solution 1:

Knight Commander Eagus is the recipient of the soup. He is the one who trains you with the sword at the start of the game, and is located at the knight academy, inside the sparring hall.

Here is a picture of him (image source):

Here's a video showing the outside of the sparring hall if you cannot recall what it looks like, or where it is:

Solution 2:

It's the Knight Commander, the man in the Sparring Hall that you got the sword from. If you failed to deliver it to him in time, try giving it to him anyway or see if you can buy a bottle.

Knight Commander Eagus:

The image is from his page at IGN.

Solution 3:

You are supposed to deliver it to Commander Eagus, in the Sparring Hall (where you got your sword from, and were taught how to use it).

However, there is a 5 minute time limit after which the Pumpkin Soup will go cold, which you have likely exceeded at this point.

Solution 4:

Knight Commander Eagus is who you deliver the soup to. He is the man you got the training sword from to go rescue your Crimson Loftwing.