But is it wrong? I find 32 200 000 results on google just for "på hvem som * er" so I believe it's used commonly enough...I also came across this sentence later in the course
Alle voksne med norsk statsborgerskap kan velge hvem som skal representere dem på Stortinget.
I would have expected that when a relative pronoun like hvem, hva, etc. is the subject (s) in a rel. clause, e.g.
Jeg lurer på hva (s) som skjer.
som is required, and when hvem/hva/etc. is the object (o) in a rel. clause, e.g,
Jeg lurer på hva (o) han (s) har gjort.
som is not allowed.
It sounds like there is some freedom in using som, though, at least in the former case. Is that right?
Another question that would help—this might be the source of my confusion—if someone asks a Norwegian, "Hvem er du?" would the correct answer be "Jeg er jeg!" or "Jeg er meg!" I'm expecting the former to be correct, but it sounds like the latter is.
In this particular sentence, "Hun lurer på hvem han er", it would not be grammatical to use "som". I would compare it to saying "She wonders who he is" vs "She wonders who that he is".
However, you can absolutely use "hvem som" in an overwhelming amount of sentences in Norwegian, such as the examples you showed above! "som" is often used to join a dependent clause to an independent clause, and can convey different meanings. I'm sure the "tips and notes" section covers this, but some of them are:
-In order to compare: "Hun er så høy som ham" -> "She is as tall as him" -To exemplify: "Land som Norge.." -> "Contries like Norway.." -To describe a condition: "Kom som du er" -> "Come as you are" -To introduce a relative clause: "Mannen, som bor her, er borte" -> "The man, who lives here, is gone"
(You can find more here, it's written in Norwegian, though: http://www.nob-ordbok.uio.no/perl/ordbok.cgi?OPP=+som&begge=+&ordbok=begge)
Regarding "Jeg er jeg" vs "Jeg er meg" then the latter (meg) is correct. "Jeg" stands as subject, whereas "meg" functions as object in the sentence and would have to be the object form: Jeg - meg, I - me du - deg, you - you hun - henne, she - her
and so on. I hope this answers your question! Feel free to ask if something is unclear, and do add something if anyone else wants to!
'Who' (and 'hvem') is not a relative pronoun here, it is an interrogative pronoun.
To see this, if you were talking about an object rather than a person, you would say 'She is wondering what it is' not 'She is wondering that it is'