you can try to use django-mathfilter for this purpose.because javascript can be disabled by the user and django-mathfilter is so powerfull.

$ pip install django-mathfilters

Then add mathfilters to your INSTALLED_APPS.

then in you template you can just do something like this.

{% load mathfilters %}
........
{% with s_books.count as s_book and g_books.count as g_book %} 
<div id="sch-books" class="h6 mb-1">School copies - <b>{{ s_book }}</b></div>
<div id="gov-books"class="h6 mb-1">Govt copies - <b>{{ g_book }}</b></div>
<div id="total">{{ s_book|add:g_book }}</div>
{% endwith %}

for more information read this https://pypi.org/project/django-mathfilters/

Instead of involving the js script, I will recommend creating total_value on the Django side and moving it to the template.

<div class="h6 mb-1" data-count="{{ s_books.count }}">School copies - <b>{{ s_books.count }}</b></div>
<div class="h6 mb-1" data-count="{{ g_books.count }}">Govt copies - <b>{{ g_books.count }}</b></div>
<div>{total_count}</div>

I am not sure which way you follow to render the template, but should look at this one

# views.py
from django.shortcuts import render

def render_users(request):
    g_books = {}
    s_books = {}

    context = {
        "g_books": g_books,
        "s_books": s_books,
        "total_count": g_books.count + s_books.count
    }

    return render(request, 'books.html', context)

val() returns value attribute like in <input type="text" value=something/> and html() returns the content (innerHTML) of selected element.

So modify your codes like this and you are good to go. (I am assuming that django returns a numeric value in {{ s_books.count }} and {{ g_books.count }}).

$(document).ready(function()
{
    var sch = $('#sch-books b').html(); // added b element  and calling html()
    var gov = $('#gov-books b').html(); // added b element  and calling html()
    
    var total = parseInt(sch) + parseInt(gov); // converted the string into number using parseInt()

    $('#total').text("Total : " + total); // worked

});