What are the best foods to give a Wren?

We buy a large quail block.  Several birds feed daily on it, including cactus wrens.

Eurasian wrens eat mostly insects, especially larvae.  So you might try meal worms.  Put some dry oatmeal or other meal with the meal worms so they can eat while they wait, and the situation will look more natural to the wren.  I don't know for sure, but I would think they would eat them.

They don't usually go to bird feeders, but you can see if the wren will take meal worms from a dish?  I'd put the dish on  table or somewhere off the ground.

i would ask the vet this question

There are about 90 different species of Wren, all with different diets.  You'll have to more specific.

Eurasian Wrens are insectivores.  If you have a healthy garden, it will find its own food easily.