How can I migrate mysql_fetch_array to $wbpdb?

You didn’t need to post all that code to wade through! The problem is here:

<?php 
    global $wpdb;


function get_tag_data2() {

You need to global inside the function – that’s the point of global:

<?php

function get_tag_data2() {
    global $wpdb;

    // Original function code
}