Apple Watch shows only new message from whats app user but not the message itself I have an Apple watch (2016, V1) and a friend have an Apple watch (2016, v1).

On my watch it shows the message directly on the watch. As you can see here:
"Person sent you a message: Hey" (Answer Button)

On my friend's watch it shows only that there is a message. And he can click on answer. But on what should he answer? 
"New message from person received" (Answer Button)

This settings are the same on our both devices.
We enabled whats app notifications in notification center and in the apple watch app.

Do anyone know what my friend must change to see the messages on his watch?
Check your WhatsApp settings (within WhatsApp app itself), and under Notifications, ensure to turn on the 'Show Preview' option (or equivalent, since I don't know how it is spelt in your language).