Why bother?
All they will do is softball it so he does well. Give him the answers. Or just let him do it then say he did great.
Besides cognitive tests aren't actually proof of anything and there is no real science behind it. They are like an iq test, there are thousands of versions that aren't actually proof of anything and aren't the same for everyone. You can't qualify a cognitive test.
Even working in a hospital they had dog it I've tests for elderly patients like asking them to spell "world" backwards and such that didn't conclude anything, all they did was help paint a portrait of the person's state of mind. It was just part of a lot of factors that just "gave an idea" but didn't conclude anything.