That PDF document may be out of date... I just tried using gatttool on my SensorTag and got button notifications with the following command: char-write-req 0x6c 0100
I'd stick with just the TI wiki for the SensorTag as it's probably more likely to be kept up-to-date. The wiki says you only need to do that "test mode" step if you want to get notifications when the side button is pressed (because normally it just activates the advertising).
Also, you probably have to figure out what handle to use on your specific device as every firmware will cause the handles to move around. What shouldn't change between firmwares is the UUID. Try the primary
and characteristics
commands in gatttool to get the details of the services on the device.
My primary
showed this:
attr handle: 0x005e, end grp handle: 0x0068 uuid: f000aa50-0451-4000-b000-000000000000
attr handle: 0x0069, end grp handle: 0x006d uuid: 0000ffe0-0000-1000-8000-00805f9b34fb
attr handle: 0x006e, end grp handle: 0x0074 uuid: f000aa60-0451-4000-b000-000000000000
ffe0
is the UUID of the simple key service (though the wiki says it's f000ffe0, it's not on mine). So, all the handles you want to look at are from 0x69 to 0x6d
char-read-uuid 0x2902 0x69 0x6d
will show all CCC (Client Characteristic Configuration) in that range:
handle: 0x006c value: 01 00
Setting that handle to 0100 will turn on notifications for that service.