The Wikitude SDK is available for free for evaluation purposes as a trial version. If you like to use it in a commercial, non-commercial or educational environment you need to purchase an according license. All available licenses are listed on the Wikitude website and can be purchased directly from the online store
Beside the license you can find the Terms of Service for the usage of the Wikitude SDK in PDF form.
The latest available document for the Terms of Services can be found online under https://www.wikitude.com/legal/terms-of-service-wikitude-sdk/