Clue: What the tabloids call Boris Johnson when Germany replaces British combat training site (4)
Answer: DOJO
Explanation: Definition: combat training site
 "Bojo"(what tabloids call Boris Johnson) **with** "D"(international code for Germany) **replacing**(when … replaces) B(abbrev. for "British").
Defn: …/a room or hall for training exponents of judo and other martial arts.