Hello, being in a private conversation I made a Whois, with the right mouse button on the nickname of the other person and gave error not find the nick.

Here I hit the log:
<noietaa __> jajaj
<nikoo> hehe
Noietaa No such nick - Nick not present on IRC
Noietaa End of / WHOIS list

If it worked the Whois on public channel ...
Looks like the Whois does not recognize the "_" at the end of the nick

Noietaa vs noietaa__
It is normal?

<noietaa __> has a space between "noietaa" and "__", so it is not a valid nickname.

I'm not sure how you managed to receive a private message from such a person with an impossible name containing a space.