The best would be to offer to be supportive and a hearing ear IF they ever want to talk ... about anything.
WT has well programmed JWs to ignore their doubts and reject negative info regarding the religion, but simply put faith that God chose this organization and GB as his earthly representatives. Even if what is taught doesn't make sense or is opposite to what was taught a short time ago, the GB attribute that to increased understanding as supported by God's arrangement. Any opposition to this is equated to opposition to God and 'the truth'.
Although you may want to wake JWs up to the real truth about the org, until a JW comes to the realization there is something wrong and starts to question matters for his or her self, there is nothing you can say that will force them to accept what you say and any attempt will cause them to turn against you.