Zmrzlina is right, both are totally acceptable. However, the language council Språkrådet recommends writing them as two words because the stress is on the second word + because there are two words of this type that cannot be written together: i övermorgon (the day after tomorrow) and i förrgår (the day before yesterday). Therefore, we have tried to write them separately everywhere in the course, but always accept the other version too (except for the two special cases of course).
It's the [ɧ] sound, not a [sk] sound.
The rule is that sk is pronounced as [ɧ] before 'soft' vowels eiyäö and as [sk] before 'hard' vowels aouå. (the rule is broken for instance by some loan words like skelett 'skeleton' where sk sounds like [sk] anyway. )
PS I think the r is usually just not heard in this word, but it might either be heard, or combine with the ɧ sound so some people will use a [ʂ] sound instead, or some sort of combination. But anyway, no [k] sound.