For some reason this is not available in V6 and V7 docs, I will notify the team, but you can find it here for now - https://forge.autodesk.com/en/docs/viewer/v5/reference/javascript/markupscore/
I am searching documentation for the Autodesk.Viewing.MarkupsCore extension in the viewe V7, but I can't found it .
https://forge.autodesk.com/en/docs/viewer/v7/reference/Extensions/
Just I found in the viewer V2 : https://forge.autodesk.com/en/docs/viewer/v2/reference/javascript/markupscore/
For some reason this is not available in V6 and V7 docs, I will notify the team, but you can find it here for now - https://forge.autodesk.com/en/docs/viewer/v5/reference/javascript/markupscore/