How to retrive data using Json and Jquery

At least response.bookings can be either an object or an array. if you what to find you what is you case just run console.log(response.bookings); and check the debugger console.

As an object it could look like (i added some fictional fields):

var response = {
   status: 'ok',
   bookings: {
   //index: booking
       a: {seat_id: 1, user_id: 4, paid: true},
       b: {seat_id: 2, user_id: 3, paid: false},
       c: {seat_id: 3, user_id: 2, paid: true},
       d: {seat_id: 4, user_id: 1, paid: false}
   }  
};

//$.each means that function is called of each entry of response.bookings
 $.each(response.bookings, function(index, booking) {
     // frist run index='a', booking={seat_id: 1, user_id: 1, paid: true} so booking.seat_id=1
   //second run index='b', booking={seat_id: 2, user_id: 2, paid: false} so booking.seat_id=2
   // third run index='c', booking={seat_id: 3, user_id: 3, paid: true} so booking.seat_id=3
   // fours run index='d', booking={seat_id: 4, user_id: 4, paid: false} so booking.seat_id=4
   sc.status(booking.seat_id, 'unavailable');
   // you can check the values by using console again:
   // console.log(index);
   // console.log(booking);
 });

As an array it could look like (i added some fictional fields):

var response = {
    status: 'ok',
  bookings: [
  // array of booking object (index incrementel starting from 0)
    {seat_id: 1, user_id: 4, paid: true},
    {seat_id: 2, user_id: 3, paid: false},
    {seat_id: 3, user_id: 2, paid: true},
    {seat_id: 4, user_id: 1, paid: false}
  ]  
};

//$.each means that function is called of each entry of response.bookings
 $.each(response.bookings, function(index, booking) {
     // frist run index=0, booking={seat_id: 1, user_id: 1, paid: true} so booking.seat_id=1
   //second run index=1, booking={seat_id: 2, user_id: 2, paid: false} so booking.seat_id=2
   // third run index=2, booking={seat_id: 3, user_id: 3, paid: true} so booking.seat_id=3
   // fours run index=3, booking={seat_id: 4, user_id: 4, paid: false} so booking.seat_id=4
   sc.status(booking.seat_id, 'unavailable');
   // you can check the values by using console again:
   // console.log(index);
   // console.log(booking);
 });

in general is $.each only a jquery version of an for loop. Here how you can do it using plain javascript (maybe helps you to unterstand ):

// response.bookings is an object
 var booking;
 for (index in response.bookings){
     booking = response.bookings[index];
   sc.status(booking.seat_id, 'unavailable');
   //console.log(booking);
 }

 // response.bookings is an array
 var booking;
 for (var index = 0; index < response.bookings,length; index++){
     booking = response.bookings[index];
   sc.status(booking.seat_id, 'unavailable');
   //console.log(booking);
 }