I dont know if its compatible...but the only eMMC adapter I know is the one from Hardkernel (Odroid Computers),
which is a eMMC to MicroSD adapter:
http://www.hardkernel.com/main/products/...5415955758
and here is a picture of the backside from the Pinebook eMMC (seems to match) :
which is a eMMC to MicroSD adapter:
http://www.hardkernel.com/main/products/...5415955758
and here is a picture of the backside from the Pinebook eMMC (seems to match) :