Open "newfairs.com" in Firefox. Right click of a page element and choose "inspect element", for example, here is <p class="one-line">. Right click it and choose "New Attribute", add id="mytarget".

In console, input Blaze.getView(document.getElementById('mytarget')) and press Enter. You get

Object { name="Template.productListItem",  _callbacks={...},  isCreated=true,  more...}

Now you know this element is defined in template "productListItem".

Because ag can't search text in git submodule with ag Template.productListItem directly, search 'Template.productListItem' in all packages with

git --no-pager submodule foreach --recursive 'ag Template.productListItem'

Discussion

Where does Blaze come from? When connected with the web server, the browser receives many JavaScript files. All html code is generated dynamically from these js files. And Blaze is defined and loaded in these files, too.