(Author's writeup)

Tools:

host, nmap, tftp, https://www.rapidtables.com/convert/number/hex-to-ascii.html

Solution:

1) Resolve Europe.jetsons.tk
2) Scan the host (nmap -sU -p1-100 194.210.128.233)
3) Retrieve flag.txt from the tftp server (tftp 194.210.128.233; verbose; flag.txt) [NOTE: tftp client works from Kali Linux]
4) The file has this string: 666c61677b5377616e736561497357616c65734361706974616c7d
5) It’s an hexadecimal string, so use a HEX to ASCII converter

Flag:

flag{SwanseaIsWalesCapital}