Firstly, with NMEA2000, you can have multiple sensors of the same type on the
network. So no problems with installing a depth
sensor in both hulls of your catamaran and another in the stern. Each device on the
NMEA 2000 network has a unique id, and as part of the address mechanism used on the
NMEA 2000 network, each device has a unique address.
The potential difficulty will be in configuring a display, albeit a MFD/Chartplotter or a simple instrument display, with multiple depth screens, each one using the different depth
transducer as its source. You will need to do your homework. Alternatively, if you have multiple instrument displays, configure one to use the port hull
transducer as its depth source, and configure another to use the starboard hull transducer as its depth source.
Secondly, with regards to diagnostics, the most basic tool is a multimeter. At a basic level you need to be able to measure 12v DC on the NMEA 2000
power pairs and be able to measure 60 ohms resistance across the CAN-H and CAN-L pairs. Each end of the NMEA 2000 network is terminated with a 120 ohm resistor. Here is a link to a good video illustrating diagnostics on the CAN bus.
More advanced diagnostic tools, some of which include the ability to check the voltage and resistance, include those from Maretron and Actisense. For example the Actisense W2K-1 (NMEA 2000 -> NMEA183
WiFi Gateway) supports their diagnostic tool (Actisense i) and their NMEA 2000 data viewing tool (EBL Reader.)
The device mentioned in the previous post also looks promising.
Finally, if you want to "roll your own", an inexpensive Raspberry Pi, with a compatible CAN Hat such as the Waveshare or Pican-M, coupled with the canboat
software can provide both real-time and offline decoding of NMEA 2000 data.