Hello, there are modules for that in case you just want that small clock type screen most POS have.
https://www.google.com.do/url?sa=t&source=web&rct=j&url=https://apps.openerp.com/apps/modules/8.0/pos_customer_display/&ved=0ahUKEwj-gOnnz4vLAhVF9h4KHW7mD64QFggZMAA&usg=AFQjCNGWHRXkpF0EmAGwqHgecnx9cyG8eA&sig2=4N5RWx_Sqmatinf-Ebl4iQttps://www.google.com.do/url?sa=t&source=web&rct=j&url=https://apps.openerp.com/apps/modules/8.0/pos_customer_display/&ved=0ahUKEwj-gOnnz4vLAhVF9h4KHW7mD64QFggZMAA&usg=AFQjCNGWHRXkpF0EmAGwqHgecnx9cyG8eA&sig2=4N5RWx_Sqmatinf-Ebl4iQ
https://www.google.com.do/url?sa=t&source=web&rct=j&url=https://apps.openerp.com/apps/modules/8.0/hw_customer_display/&ved=0ahUKEwj-gOnnz4vLAhVF9h4KHW7mD64QFggbMAE&usg=AFQjCNFPBh3VoOhoGC9LZ7sgO0uMqp3wrA&sig2=5jtW2HZ592Y6pxU2I1mcDw
In the case you want a full monitor you could have a dual monitor setup with same image on both.