In New Zealand workplaces being able to communicate and interact with colleagues and the boss is very important if you want to fit into a team. Most new migrants find this a challenge, especially when it's the boss who greets them.
Wait for the next lift
Not worry about it - John will understand.
Make an effort. Maybe ask John if he is having a good day, or say something about the weather
In New Zealand workplaces talking to senior managers is normal. Saying nothing or waiting for the next lift could be considered strange - even disrespectful. Whenever someone greets you, try to smile and meet their eyes. Small talk such as, "How is your day?" or a remark about the weather is all that is required. Make sure you speak clearly and not too softly.
In New Zealand workplaces talking to senior managers is normal. John may not take offence this once, but he might change his mind if Robert always responds this way. At a minimum Robert should look up, smile, meet John's eyes and say, 'yes - thank you' loudly enough to be heard.
Yes. Asking John about his day or saying something about the weather would be a good idea. In New Zealand workplaces talking to senior managers is normal. It's also polite to meet the eyes of the person you talk to, and to smile and say "fine, thanks" when someone asks how you are.