The most common and most likely answer to this crossword clue is the 6 letter word KORUNA
I've seen this crossword clue in Financial Times
K
O
R
U
N
A
Buddy explains!
The straight part
We know that "that’s exchanged in /Prague" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s exchanged in /prague = koruna.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KORUNA mean?
KORUNA noun- The currency of the former Czechoslovakia, divided into 100 hellers.
- The currency of the Czech Republic, divided into 100 hellers.
- The former currency of Slovakia, divided into 100 haliers.