I'd like to put in my two cents as well. After scratching my head about why template hints weren't being displayed even though the setting is enabled, I eventually discovered that the ?templatehints={key} bit does not work with urls that include pagination, ie:

https://devserver1234.nxcli.net/mycategory.html?p=1?templatehints=magento

In this case, you would need to remove the ?p=1 portion of the url.

I'd like to put in my two cents as well. After scratching my head about why template hints weren't being displayed even though the setting is enabled, I eventually discovered that the ?templatehints={key} bit does not work with urls that include pagination, eg:

https://devserver1234.nxcli.net/mycategory.html?p=1?templatehints=magento

In this case, you would need to remove the ?p=1 portion of the url.