To be honest I quite often search for a phrase or something to locate the template it seems to be used in and take it from there. I agree it'd be quite nice to see a visualisation of the templates and how they tie together, where macros are used and so forth.
When you look at what you want to edit, right click and inspect, you will see a value data-template-name="public:whats_new" this tells me that the template I'm looking at is in the public category, and that the template name is whats_new.
If I go and do this in the admin control panel, it would look like this data-template-name="admin:node_list" which tells me it's an admin template, called node_list
If it's using a macro it will look something like this admin:sylphian_backup_macros::backup_row. This tells me in the category admin, there's a template called sylphian_backup_macros and it's using the macro backup_row to render that content.