i just dropped my actual playthrough because i killed jon ( he was a lord and he didnt want to join me)
i want to add him to my party, so ill start a new game, what its the best way to get him? i give troops to the free folk, to make them capture them?
also, if i just go and capture kingslanding and defeat joffrey ill get the kingsguard? or i need to wait to someone capture them?
That is not the easiest way.
The easiest way is to modify a different companion to be your Jon Snow, via the export/import character feature. That way you can create yourself ANY companion character you wish.