Hello,
Currently, you can find item relationships between hosted feature layers and tile layers published from them and hosted feature layer views and the source hosted feature layer. This is the first step in providing more insight into where your content is being used in ArcGIS Online.
The only sure fire way to check for your layers in other items like web maps is to parse through all of the web map text for public items in ArcGIS Online. We are actively working on projects around this problem and encourage you to upvote this idea to show your support and view updates: https://community.esri.com/ideas/7244
-Kelly