You must right click on the Notezilla icon next to the clock in the taskbar. See the exact icon in the below picture.
Also you can search sticky notes using the search option indicated below for global search. You can choose Notes Browser from the same menu.
In the Notes Browser window itself, at the bottom, you will find Advanced Search button from where you can search for any string throughout Notezilla .
You can also check this video on search feature for more clarity: