Honeymoon
noun, の adjective
You know that 旅行 is a trip. The other part is new marriage. What's the trip you go on after a new marriage? The honeymoon!
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
新婚旅行はいつ行くんですか？
When are you going on your honeymoon?
新婚旅行の日程はまだ決まっていません。
The schedule of our honeymoon hasn't been decided yet.
新婚旅行でハワイに行ってきたんです。
We went to Hawaii for our honeymoon.