Thanks
If you're looking for the connector Nordic uses for the Debug OUT header (P19), you would be looking for the Samtec FTSH-105-01-F-DV-K Digikey has them: Samtec FTSH-105-01-F-DV-K
If you're just looking to connect your external debugger (ie. J-Link, U-Link, I-Jet, LPC-Link2, Olimex, etc.) then you need a 20 pin (2.54 pitch) to 10pin (1.27 pitch) adapter. Olimex is the least expensive I've found so far. Mouser has them: Olimex ARM-JTAG-20-10
One last thing... Nordic for whatever reason has decided not to get their headers with pin 7 removed. In case you don't know this already, debug headers often has the pin 7 removed which serves only as a key to properly orient the connector. You may run into the case where your 10-pin JTAG/SWD ribbon cable has position 7 plugged, which won't work for the Nordic dev boards. I'll fill you in on a lesser known piece of info... you can remove the plug! Take a really fine pair of tweezers or a needle point and pull/pry it out. Once the plug is removed, you're good to go!
Cheers!