Watch the play
Here is the Original National Theatre Production which used Stephens' script.
Part One: 0.00.00 - 1.15.20
Part Two: 1.35.30 - 2.34.00
Maths Appendix: 2.35.35 - 2.39.15
Here are a couple of links to articles in which Mark Haddon discusses the kind of person Christopher is. They are about his novel, but they contain information about Christopher you will find useful in your essay on the play.
Mark Haddon on the origins of The Curious Incident (penguin.co.uk)
asperger's & autism | mark haddon
Resources to help you study the play
An interview with Mark Haddon, who wrote the novel the play is adapted from.
An excellent interview with Simon Stephens, who adapted the novel, Marianne Elliot, who directed the first production, and Alex Sharp, who played Christopher on Broadway.
Mr Bruff is a teacher who makes lots of excellent videos for students of English Literature. Here are his videos on this play.