The markup for a citation is double question marks. The em dash character is part of the rendering.
??citation??
For instructions, refer to the Atlassian help page:
https://confluence.atlassian.com/conf613/confluence-wiki-markup-964960693.html
Confluence renders the double question marks as follows in the XHTML:
<p> Here is a </p> <p> <cite>test</cite> </p> <p> of the citation markup. </p>
If you want the citation to be inline, rather than a separate paragraph, you can remove the paragraph breaks around the citation, in the Source Editor.
<p> Here is a <cite>test</cite> of the citation markup. </p>