Hi, 

There seems to be a bug but also a workaround. 

To create a dynamic domain, you need to 

1) You need to have 2 many-to-one fields. One for "Cliente" and one for "Contacto del Cliente". Both are using the "Contact" model.

2) Create your domain as you did but than you change it (in the black window below the fields) and you replace the double quotes with single quotes: 

[["parent_id","=","partner_id"]] shall be [['parent_id','=','x_studio_many2one_field_contact']]

=> note: x_studio_many2one_field_contact is the name of the field "Cliente"

3) Now, activate the debug mode and click on "View" (left - top) and on "XML". Now you need to locate your field in the right file. Once you located it, modify it from 

[['parent_id','=','x_studio_many2one_field_contact']] to domain="[['parent_id','=',x_studio_many2one_field_contact]]"(remove the single quotes only for x_studio_many2one_field_contact)

The domain should work now, but you will get an error if you try to modify the domain using the wizard. To modify the domain later on, you need to do it in the XML-view. 

Best regards,