If you are using the latest version you can select data through the Feature Selection window. in that case Wekinator will be receiving all data that you tick in the ML column.
A pop up message that appears when overing with the mouse each feature will tell you how many values Myo Mapper is sending to Wekinator and their type.
For more detailed info and some tips for using Myo Mapper with interactive machine learning (like Wekinator), you can refer to this paper, where there is also a detailed description of the software and examples of applications.
If then you are using the version 2.x Myo Mapper sends all messages at once. So select one only message in Wekinator.
In the Myo Mapper Wiky you will find detailed info about the OSC messages (tag, values no., values type)