Hi @ZsPapp,
Hi from Kansas! 
I believe the issue here is that you are trying to apply a table format to a field (collectionobject.catalogNumber) rather than mapping to the (formatted) table field itself (collectionobject.).
I defined a table format as described by @bhumikagupta, and once I did so, I was able to map the http://rs.tdwg.org/dwc/terms/catalogNumber term to the 1.collectionobject. string ID (corresponding to the ‘(formatted)’ Collection Object record itself).
See my DwC mapping line below:
<field term="http://rs.tdwg.org/dwc/terms/catalogNumber" stringId="1.collectionobject." oper="8" value="" isNot="false" isRelFld="false"/>
Output:
| occurrenceID | catalogNumber | originalCatalogNumber | eventDate |
|---|---|---|---|
| db191bf1-1ed3-11e3-bfac-90b11c41863e | NHMD000037319 | 37319 | 10/17/2005 |
| db191eef-1ed3-11e3-bfac-90b11c41863e | NHMD000039946 | 39946 | 06/26/2007 |
| db19207b-1ed3-11e3-bfac-90b11c41863e | NHMD000040682 | 40682 | 07/26/2010 |
| db1921e0-1ed3-11e3-bfac-90b11c41863e | NHMD000028892 | 28892 | 07/18/2001 |
The prefix appears before the catalog number itself!