Solution:
You can use PHP json_encode
function to convert PHP array to jQuery object.
Then you can use jQuery.inArray
to check if couponCheck is present in the Javascript object.
$couponCheck = get_field('coupons');
wc_enqueue_js(
"jQuery(function($) {
// On coupon change
$(document.body).on('updated_checkout', function(){
var couponArray = " . json_encode( $couponCheck ) . ";
var couponCheck = $('.woocommerce-remove-coupon').attr('data-coupon');
if(jQuery.inArray('couponCheck', couponArray)) {
$('.gift-with-coupon').show();
alert('Funziona.');
}
});
});"
);