You should have to define a data store like this:
Ext.create('Ext.data.Store', {
model: 'Employees',
storeId: 'myDataStore',
proxy: {
type: 'ajax',
url : 'path/to/your/json/file/Employees.json',
reader:{
type:'json',
root: 'employees'
}
}
});
and load it somewhere.