Hi,
We had dedicate KSDK package for TWR-POS-K81 which is under NDA. So for your case, if you are not for specific to the Point-of-Sale enablement for the TWR-POS-K81 board, you may use the examples for TWR-K80F150M or FRDM-K82F board in the mainline KSDK release.
I also attaching the sample code for K80 QSPI for your reference.