I have a friend travelling and he will be taking his goddaughter to Disneyland Paris. She is a minor.
What kind of documentation does he need to travel with her? (He is not officially her tutor or anything like that.)
He will travel inside Europe from Portugal and will travel through Brussels (destination airport).
There are specific requirements per country in EU. EasyJet has a good page on that.
Note that minors (< 18 yo) flying from Portugal are covered by one of the specific entries in the page I linked.
UPDATE: Starting from 15 JAN 2017, a specific authorization is required for French minors, when the leave the French territory without one of their parents (or the legal representative)
You didn't specify nationality although it doesn't matter much: you need a letter signed by
every non-accompanying person or organization with the legal right to make major decisions for the child
from http://travel.gc.ca/travelling/children/consent-letter . This page has links to handy letters you can fill out, sign and carry.
When I sent my minor children abroad alone, I always gave them notarized letters of consent. No official at any American or European border ever asked to see any documentation beyond their passport.
I would treat this situation as the girl traveling alone -- having an adult "with her" in some official capacity would make the situation more complicated -- and if I did persist with the letter, add the godfather under "contact information".
I would also consider giving a medical power of attorney to the godparent, just in case of either real medical emergency or some over-eager border guard questioning a man traveling with an unrelated teen-aged girl.
