Source:
United Nations Office on Drugs and Crime (UNODC): Global Report on Trafficking in Persons 2018
--> Share of detected victims by area of origin and detection*, 2016 (or most recent)
* Estimate based on 16,159 detected victims whose citizenship was reported by 90 countries.
Link:
https://www.unodc.org/documents/data-and-analysis/glotip/2018/GLOTiP_2018_BOOK_web_small.pdf