What exactly was your question?

Retina, 13 11 bytes

!`[^.?!]*\?

Try it online!

!`       print all matches
[^.?!]*  any number of non-ending-punctuation symbols
\?       followed by a question mark

Thanks to @MartinEnder for 2 bytes!

Python, 46 Bytes

import re
f=lambda s:re.findall("[^!?.]*\?",s)

Call with:

f("your string here")

output on tests:

['Can u please help me,or my friends,with formatting this question    ?', 'Can u please help me,or my friends,with formatting this question    ?', ' Huh?', ' Could you repeat that please?', ' plz can i haz cheesburgr?', 'd?', 'Does this question have a question mark?', '9 percent of cases?', 'A?', ' b?', ' c?']

another idea, 77 bytes (in python3 you'd need a list around filter):

import re
f=lambda s:filter(lambda x:x[-1]=="?",re.split("(?<=[\.\?!]).",s)))

I'm new to this so this, so this could probably be much shorter.

-17 (!) bytes thanks to Martin

-2 bytes by matching anything that is not "!","?" or "." (Getting close to the shell solutions, but I doubt I could save much more)

JavaScript, 35 24 bytes

a=>a.match(/[^.?!]*\?/g)

Returns all substrings that start after a ., ?, or ! (or the beginning of the text) and end in a ?.