It’s a bug in the Wire.h file for the WIO Terminal. The WIO Terminal uses their own Wire.h file which does NOT have BUFFER_LENGTH set.
For example the Arduino UNO version of Wire.h looks like the following:
The WIO Terminal Wire.h version in C:\Users{username}\AppData\Local\Arduino15\packages\Seeeduino\hardware\samd\1.7.6\libraries\Wire that installed with the Board Manager looks like this:
You could set your own #define BUFFER_LENGTH 32 in their Wire.h and it does compile… though it is a hack to do so as we don’t know if that is the true buffer length (it is probably larger).
I would post this as a bug on Github (or here).