I have required to send POS Receipt to customer while validating POS order, the challenge is ticket is defined in point_of_sale/xml/pos.xml 
receipt name is <t t-name="PosTicket"> 
how can i send this via email to customer.
You can create a wizard at the time of validation of POS order which popup after validating order. In that popup enter mail id of customer and by submit that receipt is directly forwarded to that customer.
Send POS Receipt Email to Customer While Validating POS Order