Hi @indrajeetma ,

3 ways you can achieve this

create an onLoad Client script

function onLoad() {
    g_form.setLabelOf('work_notes','Place holder work notes and label');
    g_form.setLabelOf('comments','Place holder comments and label');
}

this would also update the label like

OR

create an onLoad client script with Isolate script as false

function onLoad() {
    setTimeout(function() {
        $('activity-stream-work_notes-textarea').placeholder = 'put work notes place holder text here'; // update with your place holder text
        $('activity-stream-comments-textarea').placeholder = 'put comments place holder text here'; // update with your place holder text
		
    }, 1000);
}

update the placeholder text as per you requirement

other way is by updating the field label

go to the work_notes dictionary and create a new Label record with incident table name and element is work_notes (follow the same for comments)

whatever you set as label it will reflect in the place 

Please mark my answer as helpful/correct if it resolves your query.

Regards,
Chaitanya