It depends what sort of navigation bar do you use.
If your navigational control is html then add
runat="server" attribute to its tag and on code behind you add something like this:
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
this.yourNavigationControl.ServerClick += (s, evt) =>
{
};
}
}
If your navigation control is WebForms control, then it is even simpler.
Most controls (if not all) used for navigation have some sort of click event - use that!
protected void NavigationButton_Click(object sender, EventArgs e)
{
}
protected void MenuItemClick(object sender, MenuEventArgs e)
{
}