The top button. I pair it. It might work once opening OneNote, it might not. Even if it works once it stops working after and never works to wake it from sleep. The MS store replaced the pen and the new one had same problem. Then they replaced the SP3. Both have the same WiFi limited connectivity problem (at some places at work) and pen top problem.
But the bottom line is the WiFi works fine at home (may have to reboot after coming home from work with it in standby) and in some places at work and the pen writes fine so neither problem keeps me from loving the SP3. It's thinness and weight and screen resolution along with core i7 and 8GB RAM make me glad I got it to replace my core i5 4GB SP1, even with these problems. I just wish the pen button opened OneNote from sleep, as advertised, because I use OneNote at work as a white board to jot down diagrams and graphs for teaching.