1. I went on a school field trip to Jeju Island.

2. I went on a school trip to Jeju Island.

3. I went on a study trip to Jeju Island.

4. I went on a study tour to Jeju Island.

5. I went on a study travel to Jeju Island.

6. I went on a field trip to Jeju Island.

(Which expressions are grammatical? Students go to places far off and they spend about 3 days traveling here and there to learn lots of things.)

2 answers

#5 is a bit unusual, but the rest are all perfectly fine.
The answer is number 1.