Final answer:
Charles Wallace's special gift is his extraordinary intelligence and the ability to communicate telepathically, which is called kything in 'A Wrinkle in Time'.
Step-by-step explanation:
The special gift that Charles Wallace has in Madeleine L'Engle's novel 'A Wrinkle in Time' is his extraordinary intelligence, which includes the ability to understand complex concepts and languages at a very young age.
Additionally, Charles Wallace can communicate telepathically, a talent known in the book as kything. This allows him to connect with others on a deep, non-verbal level, profoundly understanding their thoughts and emotions.