杨某不胜感激各位的回答 ！😃

The verb “look at” is a phrase and always needs “at” before the object. In your example, “down” is used to show the direction — apparently “he” is in a lower position than the speaker. Here, “down” has its literal meaning. On the other hand, we could saying “looking down on him”, where “to look down on someone” means to regard someone as inferior (i.e., not as good).

Depends on the whole sentence, here you can have two phrases, either "looking down at" or "looking down at him" so yeah

You are correct.. looking down at him was correctly used. Practice makes perfect, your question is not stupid. 👏

Totally agree with the other two answers, just wanted to say - there are never any stupid questions!!