I bought Ultra96 V2 development board and the training packet in the https://www.avnet.com/wps/portal/us/resources/training-and-events/event/ultra96-technical-training-courses/ . When I tried to implement SDK applications, i can't boot the board with JTAG mode. It keeps giving "Launch error", It seems that it can't find the board that way. Hovewer UART communication works fine.
I am not sure I recall a lab in the TTC that has you boot from JTAG.
The instructions should be very clear how to do that if that is the case.
Regardless, if you are booting from JTAG, you must select that prior to powering on the board - otherwise security settings will lock that out.
You can take a look at this in the User Guide on the product page under Technical Documents:
This is a snip from page 27 of the User Guide: