You can refer to following steps to transfer textures from Zbrush to Maya.
Step 1:Under Texture Map, click on New From Polypaint
Step 2: A texture map should appear on your Brush Texture.
Step 3: Then click on Export, to send it where you want it.
When importing the texture into Maya, note that your texture may be upside down(Zbrush is weird like that). You can just flip in your image editing software. There is also a way to change the export orientation in Zbrush.
Solution by: Kevin 仙 Stark, Game Designer and 3D Artist