@samadam 

so notification is triggering from workflow on CHG table.

2 ways

1) To show link to approval record you will have to use email script in workflow notification activity

<mail_script>
var gr = new GlideRecord("sysapproval_approver");
gr.addQuery("sysapproval", current.sys_id);
gr.query();
if (gr.next()) {
var sysId = gr.sys_id;
var tableName = 'sysapproval_approver'; // table name
var instance_name = gs.getProperty('glide.servlet.uri');
template.print('Click here <a href="' + instance_name + tableName  +'.do?sys_id="' + sysId + '">' + 'Approval Record' + '</a>');
}
</mail_script>

See how you can add that below

OR Another Approach

2) you can use run script to store the link in workflow scratchpad and then use that workflow scratchpad in message of workflow notification activity

Run Script:

var gr = new GlideRecord("sysapproval_approver");
gr.addQuery("sysapproval", current.sys_id);
gr.query();
if (gr.next()) {
    var instance_name = gs.getProperty('glide.servlet.uri');
    workflow.scratchpad.approvalLink = 'Click <a href="' + instance_name + tableName + '.do?sys_id="' + taskID + '">' + taskNum + '</a> to view the Task.';
}

Then use this in workflow notification message part

${workflow.scratchpad.approvalLink}

Here in below image use ${workflow.scratchpad.approvalLink} to show that link

If my response helped please mark it correct and close the thread so that it benefits future readers.