Dear Mohit,
even if this is an old thread, I'm replying here with my findings for future help in case of similar requirements.
Basically notes are store as standard texts in table STXH. You can find them using the appropriate GUID (to be inserted in TDNAME), retrieved from table CRMD_ORDERADM_H.
Table TTXID is also useful to understand the Text IDs.
After you collected all the required information, you can sue as usual the following f.m. to manipulate the notes:
READ_TEXT -> Read Text
DELETE_TEXT -> Delete Texts
Regards
Antonio