Do you want it pronounced like "edging" or "aging"?
Regardless, it's the "j sound" of "James" (as well as of both "edging" and "aging" for those of you who pronounce them the same) and not the "j sound" of "Jaques" (or the "z" sound of "azure").
(For those familiar with IPA, /be.'dʒiɲ/ not /be.'ʒiɲ/)
That is, IPA [t͡ɕ]
Edit: And if anyone's curious, there are four sounds in Mandarin that English-speakers will interpret as forms of "ch", varying based on aspiration and point(s) of articulation. In Pinyin, all four have distinct romanizations (which is one advantage Pinyin has over Wade-Giles).
Pinyin IPA Articulation Aspirated
ch [ʈ͡ʂʰ] postalveolar retroflex Y
zh [ʈ͡ʂ] postalveolar retroflex N
q [t͡ɕʰ] dual alveolo-palatal Y
j [t͡ɕ] dual alveolo-palatal N
By contrast, English "ch" is postalveolar but not retroflex, and aspiration depends on context: IPA [t͡ʃʰ] or [t͡ʃ].I don't know IPA but BAY-jing (aging) vs BEH-jing (edging).