The Wire library has a function void setClock(uint32_t frequency) to set the I2C clock frequency.

It would be useful for (library) developers to be able to read the current clock frequency so I could drive a device at maximum frequency and reset the I2C bus afterwards.

some_device_call()
{
 uint32_t prev_freq = Wire.getClock();
 Wire.setClock(_my_max_freq);
 // do my I2C thing
 Wire.setClock(prev_freq);
 return whatever;
}

The ESP32 does already support a getClock() function,

For AVR based devices it could look like

FILE: Wire.h

// class TwoWire : public Stream
...
uint32_t getClock();

FILE: Wire.cpp

uint32_t TwoWire::getClock()
{
 uint32_t speed = F_CPU / ((TWBR * 2) + 16);
 return speed;
}

Yes the value may not be exact what was set by setClock() but it would be the actual frequency.