What I can suggest is that you navigate to Administration -> Settings -> Advanced -> Toolboxes -> Toolboxes -> PageLayouts -> Sections -> Grids -> Tools
where you can see all the layout grid widgets created in the project. When you click on the grid widget you can inspect the Layout Template field to check the name of the layout file and where it is created.
You may also refer to the below article for more details about creating custom layout grid widgets in Sitefinity:
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items