Comment 3 for bug 1751634

Thank you for reply, Zygmunt!

You can check this yourself.
I have tested this on 16.04 LTS with all updates installed (see steps to reproduce above):

$ snap --version
snap 2.31.1
snapd 2.31.1
series 16
ubuntu 16.04
kernel 4.4.0-116-generic

$ snap install notepadqq
notepadqq 1.2.0-2 from 'danieleds' installed
$ sudo notepadqq
[sudo] password for me:
mkdir: cannot create directory '/run/user/0': Permission denied
No protocol specified
QXcbConnection: Could not connect to display :0.0
Aborted (core dumped)