Use data-options
readonly:true and
disabled:true
<th field= "fecha_fin_real"
fixed="true"
width="115"
align="center"
editor="{
type:'datetimebox',
options:{disabled:true,editable:false,readonly:true,currentText:'Hoy',closeText:'Cerrar',okText:'Aceptar',showSeconds:false}}" >
Fecha RealTer
</th>