The subject line lets us determine the content, so please fill it in.

Literal

Content [subject-が] subject-line [with-で] judgment can [so-ので], entry [object-を] please [humble-致します].

件名 ('subject line') is email/business vocabulary. 判断出来ます is the potential of 判断する ('to judge'). ので ('because, since') gives the soft reason. 記入をお願い致します is a polite request stacking お願い + いたす (humble する). A standard business-email instruction.