No need to use jQuery
document.getElementById("modal-login").onClick = function () {
window.location.hash = "register";
}
For example, try pasting this into your browser's JavaScrtipt console, then click on your question text.
document.getElementById("question").onclick = function() {
window.location.hash = "footer";
}
If you really want to use jQuery for some reason
$('#modal-login').click(function(event) {
event.preventDefault();
window.location.hash = "register";
});
Edit:
Your question isn't about hash locations in general, but how this modal plugin that you're using works. The following was determined by reading the source to the plugin, found here:
http://demo.pressapps.co/plugins/wp-content/plugins/pressapps-modal-login/js/modal-login.js?ver=1.0.0
http://demo.pressapps.co/plugins/wp-content/plugins/pressapps-modal-login/js/modal.js?ver=1.0.0
Here's what you need to execute to get your desired behavior
$('.your-register-button-class').click(function(e) {
/* We expect plugin's click handler to fire in addition to this one. */
$(".modal-login-nav[href='#register']").click();
});
I'm assuming that the element with .your-register-button-class also has attribute data-toggle="ml-modal".
document.location.hash = whatever