Would this be better interpreted as "why has he come back" or "remind me why he's here"?
You can say that.
What's the difference between פה and כאן?
There's no difference, they're interchangeable.
The difference is the spelling
As Danny says, they are different words but have the same meaning. פה is from biblical Hebrew, כאן is from Aramaic I think
The question was about the difference in meaning. There is no difference in spelling - they are two different words.
Can you also say למה הוא פה שוב and have it mean why is he here again? Or is that bad Hebrew?
It's ok, might change the emphasis, but not the meaning
שוב means again?
Is "פה עוד פעם..." the same meaning here?
Why is "Why is he again here?" wrong?
Wrong English. You can't put "here" after "again"
What is the difference between עוד and שוב?
ll עוד means 'more' or 'still', שוב mean 'again'. So,
Why is he here again = למה הוא שוב פה
Why is he still here = למה הוא עוד פה
You can use עוד פעם (literally "another time") instead of שוב though.
I love the way she sounds fed up, slightly disgusted but also kind of resigned to his reappearance
I see the suggestions say "Here" or "Mouth." According to the voice over I hear "Poh" for "Here", but I know "Mouth" as "Peh". Is this correct?
Correct. This is one of many such examples, where two words are spelled the same, but pronounced differently. Context is what helps us understand which is which.