Yes, a question can be restricted to a space.
Here is a detailed description of how that works from Atlassian's own documentation - this is from the Questions and Answers page (excerpt):
Sometimes a question only relates to one team or project or just shouldn't be visible to everyone. By asking a question in a space, you get the benefit of the space permissions - only people who can view the space can search for and see questions that were asked there.
To ask a question in a space, go to the space and choose Questions on the sidebar (if you can view the space you'll be able to ask and answer questions). Alternatively, you can go to Create > Ask a question and choose the right space from the drop down.
Only the question is private - topics are visible to everyone who can use Questions. For example if you ask "How much is the staff bonus this quarter?" and add the topic 'bonus-q4' in a space that only senior managers can see, other people will be able to see the topic 'bonus-q4' and that there's one question for that topic, but not the question itself.
Note: Viewing questions in a space is not available in the documentation theme (find out why), and may not be available in some third party or custom themes.
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