So, If you want to modify damages for each dose you can edit it by DB : spell_bonus_data, DBC modding isn't needed for this spell.
Find Envenom (ID 32645) or add it if it does not exist (should exist), then try to modify value in "ap_bonus", then test it.
Hope that was what you want haha.
column 53 --> Requiered Item, (Like [Soul Shard](6265) for Warlock spells)
column 61 --> Amount of requiered item (column 53)