Hello,
after some research I finally figured out which connector is the correct one to use with this EVB. First I measured which pins are connected to GND:
JTAG pins connected to GND
This implies that the oddly numbered pins 3 to 19 are GND. This rules out the 1:1 pin layout as in https://repo.lauterbach.com/adidc20a.html?product=la-3255.
The EVB manual states NOTE - JTAG – TRACE Signals
Due to the MCU ports used on the trace signals also are shared with other interfaces,
it is important to isolate these signals/interfaces for the J4-Cortex Debug D ETM
connector.
Those signals are TRACE_CLK, TRACE_D0, TRACE_D1, TRACE_D2 and TRACE_D3 which are only present in the MIPI20T layout (see https://repo.lauterbach.com/ad2729.html).
=> I've ordered the LA-2729 adapter, removed the dead-pin and was able to successfully communicate with the board using Trace32.
Hope this helps anybody!