Sons say Kaddish for their fathers and mothers for the first eleven months after their passing and every year on the anniversary of their passing (according to the Jewish calendar).

But let's say there is no son—or maybe there is, but perhaps he's been relocated by his employer to Karachi where it's not easy to find ten Jewish men three times a day. In this case, you have two options:

1. Ask another relative.

If there is no son to say Kaddish, another male—preferably a close relative—should say the Kaddish. (Some are of the opinion that first preference goes to a son-in-law.1) However, that should not be a person who has both parents still alive. If you wish to say Kaddish for someone but both your parents are, thank G_d, still in this world, you should ask your parents' permission.2

2. Ask someone else.

In a case where there is no son or relative who can make it to a minyan to say the Kaddish, someone else should be asked to do it in their stead3. This person will need to be told the Hebrew name of the deceased and the Hebrew name of the deceased's father. It is best if the relatives pay this person a stipend4. Many rabbinical colleges provide this service in return for a donation. You can also access such a service by clicking here.