Most high end Z270 motherboard should have one usb 3.1 gen 2 header.
If you looking at the I/O of the motherboards then most of them should have support for USB 3.1 gen . If it is advertised as 10gbps then it is usb 3.1 gen 2.
Note that there are different type of usb 3.1 gen 2 which support different levels of features. http://www.tomshardware.co.uk/usb-31-usb-type-c-refresher,news-51106.html
Most high end Z270 motherboard should have one usb 3.1 gen 2 header.
If you looking at the I/O of the motherboards then most of them should have support for USB 3.1 gen . If it is advertised as 10gbps then it is usb 3.1 gen 2.
Note that there are different type of usb 3.1 gen 2 which support different levels of features. http://www.tomshardware.co.uk/usb-31-usb-type-c-refresher,news-51106.html