By rooting the smartphone usually only an app (like SuperSU) to manage these rights installed is installed. However, the apps do not display ads.
However, Kingo root might install additional apps during the rooting, which might then display ads.
In a first step, you should uninstall all (Not system) apps that are not used.
If the advertisement is still displayed, further apps should be gradually excluded, for this they can also be uninstalled.
If this is about in App advertising, it may be because an update has added advertising. To remove this type of advertising, an adblocker can be installed.