You need to return the result of the query

function getCount(){
    const usersQuery = "SELECT count(id) as cnt FROM users";
    return dbConn.query(usersQuery,function(err,rows)     {
        if(err) {
            console.log('failed  to get count');
        } else {
            return rows; // retun count
        }
    })
}

Note that probably returns a Promise you need to handle correctly.

Finally I got the required output by using Promise() in node js

Code:

var express = require('express');
var router = express.Router();

router.get('/', function(req, res, next) {      
    const Query = "SELECT * FROM t1";
    dbConn.query(Query,function(err,rows)     {
        if(err) {
            // write some code
        } else {
// call to promise
              getData().then(function (outputVal) {
                console.log(outputVal[0].Usr);
            }).catch(function () {
                // write error here
            });
        }
    
    });
});

// Promise code

function getData() {
    return new Promise(function (resolve, reject) {
        //  setTimeout(function () {
        const MQuery = "SELECT count(id) as Usr FROM t2";
        dbConn.query(MQuery , function (err, rows) {
            if (err) {
                reject();
            } else {
                resolve(rows);
            }
            // }, 1000);
        })
    })
}

A couple of things you should know:

1. The functions declared outside routes will be executed first in stack once the server starts even though you haven't called the specific route yet. By the time you call this function, it already holds undefined or null depending on the code inside the functions.
2. dbConn.query() is Promise. Which means it works synchronously.

if you need count of users, here is what you can do:

router.get('/', function(req, res, next) {      
    const usersQuery = "SELECT * FROM users";
    dbConn.query(usersQuery,function(err,rows)     {
        if(err) {
            console.log('this error',res);
        } else {
            let total= rows.length // you will get an array of users, therefore the number of users is equal to the length of the array
            console.log(total);
        }
        
   });
});