Can Anyone tell me what is the default gain of Electret Microphone Amplifier 4466. I need the gain, to calculate the db SPL value.
The MAX4466 doesn't have a 'default' gain. Gain is set by the ratio of feedback and input resistors connected to the inverting input (IN-). For example if the feedback resistor is 220k and the input resistor is 22k then the gain will be 220/22 = 10, or 20dB. To determine the gain of your circuit you need to know the values of those resistors.  

SPL is rms sound pressure, so you must convert your 1.7V peak-to-peak measurement to rms by dividing it by 2.828 (assuming a sine waveform) which works out to 0.6Vrms. dB is a relative measurement, representing a power gain or loss. To convert 0.6V to dB you must first decide on a reference power or voltage level. dBV is voltage gain or loss relative to 1V. 20(log 0.6/1) = -4.4dbV.

If your amplifier gain is (say) 20dB then the mic must have generated -4.4 - 20 = -24.4dBV. The mic has a sensitivity of -44dBV, which means that it generates -44dBV at a sound pressure of 94dBSPL. In your test it generated -24.4dBV which is 19.6dB higher than -44dBV, so the sound pressure level must have been 19.6dB higher than 94dBSPL, ie. 113.6dBSPL.