How do you say how was your trip to Japan in Japanese?

いいご旅行を : ii go ryokou wo : (means) have a nice trip. "Itterasshai" can also be used, but it literally means take care, usu used when seeing someone off.

itterasshai - literally means "go and come back" and would be the typical send-off for someone going on a trip.

My parents have never said いいご旅行を to me (I'm of Japanese descent). That's very formal. You might say that to your boss, but it wouldn't be used with a friend or close relative. You wouldn't even say that to a colleague of equal or lower status.