
1 answer
I would suggest you to create a new data model for that.
You can create two new objects, namely Presenters/trainers and expertise.
There can be a many to many relationship between the two (one presenter can have multiple expertise and vice versa)
So you have to create a junction object between the two.
And then that junction object would be linked to Opportunity via Loopup/ M-D.
Hope this helps!