I was a resident of Sweden but moved after living there for 2 years. Can I move back with my minor son who holds a Swedish passport? Can I reactivate my Swedish personummer and get a duplicate card?
Can I reactivate my Swedish personummer and get a duplicate card?
When you get your Swedish personal number, it is valid for life.
Therefore, if you can get a visa or other form of permit to live in Sweden again, you can just resume using the personal number that you were assigned in the past.
However, whether you can simply move to Sweden with your son is another question — probably not, but do post the question separately.
It's unclear exactly what you're asking about.
If you lived in Sweden before and were folkbokförd (registered in the population register) then you will have received a personnummer. You keep that number for life. However, you do not keep the status of being folkbokförd for life, which is the part that actually matters. If you leave Sweden, you cease to be folkbokförd as living in Sweden and lose the rights associated with that. If you return to Sweden and later get folkbokförd again they will reopen your record and reuse the number. I'm not sure what happens to Swedish ID cards (not the National kind citizens can get from police) if you leave, I suspect they may cancel it but I'm not sure, and in any case it's only 400 SEK to get a new one.
None of that has any relevance to whether you have the right to move back to Sweden or get a residence permit, though, if that's what you're asking. If you had a residence permit in Sweden and left, it is no longer valid. If you are an EEA or Swiss national, or moving together as a family member with one, you are allowed to move back to Sweden without needing a permit though.
If your son holds Swedish citizenship then, in theory, you can move back to Sweden with them as their family member under EEA rules, but that only works if you're moving from an EEA country, which I'm guessing (from your other posts) you're not. Your best bet is probably to apply to Migrationsverket for a new residence permit based on your son's citizenship?