To start with, your familiar can't use Shocking Grasp. Find Familiar says:
Finally, when you cast a spell with a range of touch,
your familiar can deliver the spell as if it had cast the
spell. Your familiar must be within 100 feet of you, and
it must use its reaction to deliver the spell when you cast
So you use Shocking Grasp, and your familiar merely delivers it. This all happens on your turn, too, not your familiar's turn.
However, this is a good thing for you, because Thunderbolt Strike says that:
At 6th level, when you deal lightning damage to a Large
or smaller creature, you can also push it up to 10 feet
away from you.
So the fact that you cast Shocking Grasp, and you damaged a creature, means that you can indeed use Thunderbolt Strike to push it away from you.
Note that that's away from you, not away from your familiar: Your familiar delivers the spell, but you still cast it, and you dealt the damage. If that wasn't the case, you wouldn't be able to use Thunderbolt Strike at all.