Hi,
I have a feeling this is likely not the right forum to post your question, as it is specific to an add-on not developed by Laminar Research. Your best bet is to contact the ad-on developer via the X-Plane.org forum >> "Payware support" >>Airbus Airliners>>A350 by Flight Factor. In there you can post your question, and either some other add-on user or the developer will reply to your question. Maybe the GPWS readout is not implemented, or there is a specif switch to turn it on, but you will find you answer more easily in the dedicated forum.