can I trade in iphone 11 that I bought in Japan?

You can verify this by put your iPhone's serial number in the link here:

Settings- General-About (For Serial No.)

https://www.apple.com/shop/trade-in

When I did a trade in they just verified Find My iPhone was turned off then erased the device. They didn't check the serial number to see where it was from so I imagine you could. However, there's always something in the system that may flag it.

You can try.