Denodo does allow for comments to be placed in VQL queries for creating a view: they are not however, in the VQL tab after the view has been created. For long lasting comments, I would create the views graphically to be able to have descriptions of different parts of the view added in. I can see these descriptions even if the view is integrated with another view. For more information on descriptions, please check out the section [Object Descriptions](https://community.denodo.com/docs/html/browse/8.0/en/vdp/vql/language_for_defining_and_processing_data_vql/object_descriptions/object_descriptions) in the Virtual DataPort VQL Guide.
Hope this helps!