is jeg ser sjelden onkelen min or jeg ser min onkel sjelden possible?
Both are fine
why can you not say "jeg sjelden ser onkelen min"
Because the verb wants to be in the second position, following the V2 rule.
We've learned so far that possessive is not needed when talking about family members. I guess "Jeg ser onkelen sjelden" would would also be fine although it's incorrect in this excercise?
Pretty sure it's "Sjeldent"
Jeg ser min onkel sjelden means - I see my unlce rare