Can i make a filed required or disable a requirement on a filed dynamically on an event for example ?
Yep, sure, you can use disable|enable API
http://docs.webix.com/api__link__ui.view_disable.html
http://docs.webix.com/api__ui.baseview_enable.html
As for “required”, just use
$$("input_id").config.requred = true; //or false