To use the Sketch tool in ArcGIS Online Map Viewer, a user must have a Creator or GIS Professional user type and their role must be configured to User, Publisher, Facilitator, or Administrator.
Note: ArcGIS Online public account holders can create sketch layers.
Refer to ArcGIS Online: User types, roles, and privileges for more information.
Note: Features in a sketch layer are saved in the map, but not as a feature layer. Therefore, only the map author can edit and save sketch layers.