How to call the function in node js

If mysql.myFunction is undefined, then you're probably not actually exporting it:

function myFunction(resourceIdentifiers, callback){
    // ...
}

exports.myFunction = myFunction;

Function and variable declarations are "private" to the module by default. Only those members you explicitly export will be accessible from other modules.

You also won't be able to use return rows; as you're trying to. Asynchronous code is event driven and doesn't wait, which return would need it to do.

myFunction already has a callback argument and you're passing a function for the value. You just need to call it:

// ...
function (err, rows, fields) {
    callback(err, rows);
}
// ...

You should also at least escape resourceIdentifiers when concatenating.

But, generally better is to use a placeholder (?) and the optional, 2nd argument to .query():

response.query(
    'call SP_ExposePricingDetailforUI(?)',
    [ resourceIdentifiers ],
    function (err, rows, fields) {
        callback(err, rows);
    }
);

You just need to callback within the result of response.query. Something like this.

mysql.js:

function myFunction(resourceIdentifiers,callback){

    dbconnection.execute( function(err,response) {

        response.query('call SP_ExposePricingDetailforUI(' 
                                      + resourceIdentifiers + ')'
                      ,function (err, rows, fields) {
                          callback(err, { rows: rows, fields: fields});
                      });
                 }
        );
}

module.exports.myFunction = myFunction;

restservice.js:

mysql.myFunction(resourceIdentifiers , function(err,resp) {
    console.log(resp.rows);
}

Update - removed the return rows statement that I missed the first time around.