Hi Norahmf,

Hope you can clarify the following.

1. Does the Purchase Order Lines page belong to the PurchaseOrderLinePart LU? or are these 2 separate LUs?
2. Is your requirement to simply add a persistent attribute to be updatable or do you also want it to be disabled based on some condition?

Custom Attributes - Technical Documentation For IFS Cloud

1. Does the Purchase Order Lines page belong to the PurchaseOrderLinePart LU? or are these 2 separate LUs?

what meaning of Lu?

this is page I add it from here 

I need same custom attribute  showing in these two places

1. Is your requirement to simply add a persistent attribute to be updatable or do you also want it to be disabled based on some condition?    just add a persistent attribute to be updatable

Since these are 2 separate entities you will have to create 1 custom attribute in 1 entity and another custom attribute in the other entity with the same name. But if you update the field from the purchase order line page it will not show the value in the purchase order line part page/list and vice versa as these will be 2 separate custom attributes.
But you can handle this via a custom event. Example: when the attribute in purchase order line is updated then copy that value to the attribute in the purchase order line part page and vice versa.