Anki and some other platforms use a particular format to signify cloze deletions in flashcard text. It has a format like any of the following:

• {{c1::dog::}}
• {{c2::dog::domestic canine}}

Here’s a regular expression that matches the content of cloze deletions in an arbitrary string, keeping only the main clozed word (in this case dog.)

{{c\d::(.*?)(::[^:]+)?}}

To see it in action, here it is in action in a Python script:

import re

def stripCloze(searchText):
    return re.sub(r'{{c\d::(.*?)(::[^:]+)?}}', r"\1", searchText)

print(stripCloze("The {{c1::passengers::tourist riders}} spotted a breaching {{c2::whale}}."))

It should return The passengers spotted a breaching whale.