If this just happened last week, he probably is still somewhat in shock (on top of feeling ill). Processing it all is a lot. Sounds like you are doing good with what you're doing - visiting, checking in, etc. Over time, he'll have opportunities to talk. He also may prefer talking with other people who are in similar situation or professionals trained to counsel those in treatment. So definitely follow his lead. Make it clear that you are available to listen and it doesn't matter if it is serious or lighthearted.
A friend of mine (late 30s) went through out of nowhere cancer + chemo last year, though better prognosis situation. She was actually kind of bored a lot of the time (especially when she wasn't feeling miserable) and just appreciated company and/or good light entertainment ideas. We spent time watching tv together and making dumb jokes about it.
Also, I don't know if you would be the 'person' but in this kind of situation, it really helps if one point person - typically someone reliable and close with your friend's wife - who can be the calendar-keeper/organizer person for all friends and family who will be offering help, checking in, etc. Someone has to field calls/texts/emails and coordinate the schedules of which friends and family members will be bringing food or meals for wife and kids on which days, and so on. This might be getting set up already or might need a 'nudge' (if wife is still trying to do it all herself, for example). You may or may not be a good choice to be that point person. To best help your friend and his family, you might want to see if that's happening yet. If so, then help support point person and work with them to develop the systems that will respect your friend's wishes (now and as they may change over time) and make sure that the family can focus on his health, treatment, and plans for the future. If not, then maybe you can help get that underway, whether you are the point or not.