Question is in the title, thanks.
The question is not about emoticons. (In reality I’m more interested in unicode single/double quotations, en/em dashes, other specialized letters, etc.)
Nobody here has ever wanted to do this? What solutions did you find?
I think that you need to configure a compose key for that. If you’re using xfce, it would be in the “Layout” pane of the keyboard settings app.
After that, you can write various characters using compose <key_sequence>
For instance, you can write “§” via compose s o.
p.s. You need to do it in dom0, it should work in all qubes. For me it works even over remote desktop protocols.