125 kHz is 8 µs. The signal is high for 4 µs. Reading in the middle of the high level is 2 µs after the rising edge.
With an Arduino Uno, a interrupt takes at least 5 µs: https://gammon.com.au/interrupts. That is 2.9 µs for storing the cpu state to the stack and 2.2 µs for retrieving the cpu state from the stack.
When you use attachInterrupt() at the rising edge, and read a digital pin by reading a register directly, then you read the pin about 2.9 µs later than the rising edge of the signal. That is about in the middle.
However, what will you do with that information. There is not enough time to do something with it.
The 125 kHz is too high for an Arduino Uno.
To create a 125 kHz signal can be done with alternative tone() libraries, for example the toneAC library.
https://bitbucket.org/teckel12/arduino-toneac/wiki/Home