The ItsyBitsy has pins SWDIO and SWCLK broken out on the back edge of the board. You'll need a SWD cable breakout to connect the J-Link to an ItsyBitsy:
Make the following connections between the ItsyBitsy M0/M4 and the SWD Cable Breakout:
- ItsyBitsy GND to Breakout GND
- ItsyBitsy 3V to Breakout VRef
- ItsyBitsy SWCLK to Breakout CLK
- ItsyBitsy SWDIO to Breakout SWIO