How do I make "thick cooked rhubarb"
If I were to make a guess, thick cooked rhubarb would be chunks of rhubarb cooked in a sugar syrup that is thickened. (Kind of like cherry pie filling, which comes in cans.)

Here's what I would do to simulate this:


cut some chunks of rhubarb in a size that you think you would like in a pie or cobbler.
Add some water (at least a cup) and the rhubarb to a saucepan.  Add some sugar (about a cup) Cook on medium low heat until the sugar is dissolved and the sauce is boiled down to a thick syrup.
Let the mix cool, or refrigerate, and then move along with your recipe.