javascript:void() does not open the submenu

I have tested it with other template and it works. but what is the problem... something with jquery?

I don't know exactly the problem as it is only on mobile. It can be due to a mobile script used by the template but impossible for me to know what at this stage
you must contact the Joomlart team to ask why in your purityIII template you have this issue (and not in the other templates). Hope they can guide you

if needed come back to me if they give you the solution