in transaction CJ20N is possible to see list of WBS elements.
Every WBS element have own internal WBS element number.
1. How can be possible (or with which transaction) to show from WBS element (from CJ20N) an assigned internal WBS number (WBS internal number an example e.g. 00136712), please?
2. How can be possible (or with which transaction) to show from internal WBS element number an assigned WBS number (in CJ20N), please?
Thank you in advance.
The field in question with the generated number is database field PRPS-PSPNR. I am afraid that you cannot find it in any business transaction, as there is a conversion routine attached to it which always translate it to its "external" ID, PRPS-POSID, the one you see in CJ20N.
You can however see both fields in SE16/SE16N by displaying table PRPS. Just make sure you turn off the automatic conversion exit.
In SE16 it is under: Settings > User Parameters > Data Browser > Format > Respect Conversion Exit (make sure it is off).
In SE16N it is under: Extras > Change Settings > List Output Settings > Output without conversion exit (make sure it is on).
Based on this, finding the PSPNR by POSID is quiet simple. The other way around unfortunately not, because the conversion exit also applied to the value you enter as filter. A trick here is to display the whole table as ALV Grid then use column PSPNR to enter the internal number here.