When downloading and extracting the leap developer kit:
Headers:
LeapDeveloperKit_2.3.1+31549_linux/LeapSDK/include
Libs:
LeapDeveloperKit_2.3.1+31549_linux/LeapSDK/lib/x64
With this change cmake finds the SDK with
-DLeapV2_ROOT_DIR=/path/to/LeapDeveloperKit_2.3.1+31549_linux/LeapSDK/