why ejs include partials/header.ejs not working
You have to put the partials in brackets and quotes. So you should write this part
<body>
<%- include partials/header.ejs %>
<%- body %>
<%- include partials/footer.ejs %>
</body>
Like this
<body>
<%- include ("partials/header") %>
<%- body %>
<%- include ("partials/footer") %>
</body>