Hi,

 To call new model in pos you must define it first in model.js like this:

odoo.define('your_module.models', function (require) {    
"use strict";
var models = require('point_of_sale.models');
models.load_models({    
model: 'your.model', # your model
fields: ['field1','field1'], // fields that will be used from your model 
domain: [], // domain filter
loaded: function(self,objs){     
// a function that will be executed on loading    
self.objs = objs;},});
});

you can now call your model in PosTicket xml by :

<t t-esc="widget.pos.objs.field1" />
<t t-esc="widget.pos.objs.field2" />

 Best regards.