Answer
Look at the corresponding _RPI package instead of the _REP view's own SQL — for CUSTOMER_ORDER_CONF_REP, that would be CUSTOMER_ORDER_CONF_RPI. The _RPI package is where the actual field-to-source mapping logic lives (populating the report's result data), so that's where you'll find which underlying table or view a specific _REP field is actually sourced from — for example, CATALOG_NO in this case comes from CUSTOMER_ORDER_LINE_TAB.