right site settings now showing any nintex WF option.
First the most obvious question, but someone has to ask it.
Are the Nintex workflows enabled in the site collection settings?
Second question, do you have the required permissions to work with Nintex. Setting those is a little more complicated, but pretty straightforward nonetheless.
As suggested in the previous reply, check the things. And if you have sufficient permissions you can see Nintex workflow 2013 option at gear icon.
Retrieving data ...