What is Due's ADC sampling rate ?

I have a really simple question, and i cant find the answer .
I need to know what is Due's ADC sampling rate ?

1 MHz.

Thank you ,
Is there any option to lower it to , 10Khz , 22.05 Khz , or 44.1 Khz ?

Arduino IDE has "analogRead" - command to take a single sample. To have many samples at regular time interval, you need a some kind of "driver" or library. Second things, if its audio application, you need take care about real-timing, samples must be processed with same speed as capture. Not much you can do, for stereo 44.1 you have ~160 kbytes/second, but arduino DUE could apprehend about 500-600 k. MUL + ADD, it's about 3-rd order FIR all you can get.

What i need to do is :
i'm recording Lung signal using electrical stethoscope , i need capture it real-time , during up to 20 seconds , store it and send it using serial communication , could it be done using arduino due ?

96 kbytes RAM, at 10 ksps ~10 sec. I'd say no w/o SD card shield. Writing to SD even arduino UNO could up to the job with rate 100 ksps

can you explain how to connect SD shield to the Due , and how to sample the data into the card ?

Have no idea. I've seen a thread on this forum how to store data on SD with UNO board. Try to search, box is in top-right corner