The nRF51 DK has an onboard Segger JLink, so you don't need to connect one to it. If you did want to use an external JLink, one of the full-sized ones with the 20-pin .1" pitch output, like the JLink Base or the JLink EDU, you'd use the "J-Link 9-pin Cortex-M Adapter".
For the beacon module there's no header on the board. This thread devzone.nordicsemi.com/.../ recommends the 6-pin needle adaptor, or you could solder leads on and poke them into your JLink. If you think those adaptors from Segger are insanely priced .. I agree with you.
the user guide is available for download .. I think. Either way there's nothing special about using it, you plug the USB in, you now have a JLink device which looks exactly like all your other Jlink devices, just permanently attached to the nRF52 chip (*). Everything else works just the same.
(*) you can use that onboard JLink to debug out to another board, so it's better than just attached to the one chip, but you can treat it equivalently to an external JLink you have plugged in.
the user guide is available for download .. I think. Either way there's nothing special about using it, you plug the USB in, you now have a JLink device which looks exactly like all your other Jlink devices, just permanently attached to the nRF52 chip (*). Everything else works just the same.
(*) you can use that onboard JLink to debug out to another board, so it's better than just attached to the one chip, but you can treat it equivalently to an external JLink you have plugged in.
