Question

Daniel, who / whose / whom I saw yesterday, got a
new wheelchair.

Answer 1

Daniel, who / whose / whom I saw yesterday, got a new wheelchair.

Daniel whom I saw yesterday, got a new wheelchair.

Step-by-step explanation:

You're welcome.

Answer 2

Whom

Step-by-step explanation:

Whom should be used to refer to the object of a verb or preposition. When in doubt, try this simple trick: If you can replace the word with “he”' or “'she,” use who. If you can replace it with “him” or “her,” use whom.

Who should be used to refer to the subject of a sentence.

Hope this helps!