I'm assuming that you mean Leonardo's brief codex on the subject. You really need to be specific.
It is in the Biblioteca Reale in Turin (Torino), Italy.
Please note that antique manuscripts of this kind are not regularly on display, owing to the need to protect them from light and other environmental hazards. In general, only scholars who can present the necessary credentials are allowed to examine such manuscripts in an "up close and personal" manner.
