There are several Gothic Cathedrals dedicated to Saint John (the Baptist or the Evangelist). To give you the most accurate answer, could you clarify which Saint John you are referring to, or provide more details?
However, here are some possibilities:
* St. John's Cathedral, 's-Hertogenbosch, Netherlands: This is a prominent Gothic cathedral dedicated to St. John the Evangelist.
* St John the Baptist Cathedral, Wrocław, Poland. This is another prominent example of a gothic cathedral.
If you have more details about the location (city, country) or a specific saint (the Baptist or the Evangelist), I can give you a more precise answer.