From your description, it sounds like you are trying to reference data from two data grids in a Mendix page, where each grid is contained within its own DataView.
By design, Mendix context works in such a way that it restricts access to data from one nested DataView to another. That is, you can't directly access data from two sibling DataViews. A workaround to this problem could be using a microflow that pulls in necessary data from both DataViews.
Below are the steps you can take to solve this problem:
Create a Microflow that takes the 'Workshop' and 'Delegate' as input parameters.
In this Microflow, Retrieve the DelegateIdea associated with the Delegate and the WorkshopSummarisedIdea associated with the Workshop. You can use 'Retrieve Objects' activity in the microflow to retrieve this data from the database.
Now, you have to Pass this data to your page. For that, you'll have to create a Non-Persistable Entity (let's call it 'NP_Entity') with associations to both DelegateIdea and WorkshopSummarisedIdea.
Create an object of this Non-Persistable Entity in your microflow and associate the retrieved DelegateIdea and WorkshopSummarisedIdea with it.
Then, Change the context of your page to this Non-Persistable Entity. Instead of directly placing your datagrids inside the DataView, you'll now place them inside a DataView that takes NP_Entity as its context.
Now, inside this DataView, Create two nested dataviews, one for DelegateIdea and another for WorkshopSummarisedIdea. Place your datagrids inside these dataviews. Since they are associated with NP_Entity, you should be able to access the data from both the grids.