The SDK project files have a reference to "http://nxp.com/ksdk/2.0/ksdk_manifest_v3.0.xsd" but this is a dead link on your website. Since the sdk references (appear to be) in files generated by the IDE project wizards, this seems to be an IDE issue.
We would like to use the xsd to validate our xml as well as understand the full specification for the project xml.
It seems odd to use a unavailable xml format for your IDE projects...
the http://nxp.com/ksdk/2.0/ksdk_manifest_v3.0.xsd is actually id of a namespace used in manifest file. In order to get XSD, please follow the URL placed as the second argument of xsi:schemaLocation attribute, for example http://nxp.com/mcuxpresso/sdk/sdk_manifest_v3.6.xsd as in xsi:schemaLocation="http://nxp.com/ksdk/2.0/ksdk_manifest_v3.0.xsd http://nxp.com/mcuxpresso/sdk/sdk_manifest_v3.6.xsd".