PIC 32 two I²C slave address
Have a look at the PIC32 family data sheet chapter 24. There the process of address detection is explained. It also shows (even though its not explictely mentioned in the text) that the address is in the I2C receive register after a valid address has been detected.

The code above looks like you are using the PIC32 peripheral library that comes with xc32. Look at the supplied manual there (hlpI2C.chm). It contains a chapter 'Operating as an I2C slave', which has the sample code you are looking for:

if (I2CReceivedDataIsAvailable(I2C1))
{
    slaveRxData = I2CGetByte(I2C1);
    if (I2CReceivedByteIsAnAddress(I2C1))
    {
        // Handle address byte
    }
    else
    {
        // Handle a slave RX byte of data
    }
}

if (I2CTransmitterIsReady(I2C1) &amp;&amp; more_data_to_send)
{
    result = I2CSendByte(I2C1, slaveTxData);
    // Handle sending a slave TX byte of data
}