According to dictionary.com
Word (verb: used with object) - to express in words; select words to express; phrase. Example - to word a contract with great care.
and
Demonstrate (verb: used with object) - to describe, explain, or illustrate by examples, specimens, experiments, or the like. Example - to demonstrate the force of gravity by dropping an object.
The former one will be appropriate in the context, when a person is asked to write his/her explanation or to give in written what he/she claims to be knowing.
The latter one, however, will be more appropriate in the cases, when a person in asked to physically show his/her verbal or written works.