They will focus on 2 Chronicles 36:21 and Daniel 9:2. Remember, Daniel said 'devastations' -- plural. 2 Chron talks about sabbaths DURING the time the land was desolated and how Jeremiah's 70 years were fulfilled by the Persian overthrow of Babylon addressed in that same chapter.
These are one sentence references to Jeremiah 25. To know what Jeremiah said, make them read the whole chapter. Remember when you get to the section on calamity starting with Jerusalem late in the chapter, the Society applies this to events taking place in Jehoiakim's reign -- not the Temple destruction.
This also brings us to when Daniel was actually taken from Jerusalem. He was taken before the major deportation that occurred under Jehoiachin. In Daniel chapter 1, Daniel himself claims he was taken under Jehoiakim along with some of the Temple utensils. But, the Society claims he was taken under Jehoiachin. Ask them why, since 2 Chron 36 describes two separate Temple raids -- the Society glosses over this.
Focus on one point only at first: Where in Jeremiah's 25th chapter do we find the reason to apply the '70 years' to the destruction of the Temple and Jerusalem rather than 70 years of servitude for all the nations mentioned in the chapter? No where will you find anything about Sabbath's for the land of Judah nor anything about the destruction of the Temple.
It is critical to understand how and why the Society has interpreted these verses. It takes some time to understand all this. Do not focus on the 'secular' evidence. Focus on the Bible and the Society's flawed interpretation.
Another Jeremiah point; focus on how Jeremiah 29 was written to exiles taken about 10 years before the destruction of the Temple (were they to be there 80 rather than 70 years?).
Finally, Zechariah chapter 7: These verses are NOT about the 70 Years of Jeremiah's prophecy but about what had been happening the past 70 years -- specifically, since the destruction of the Temple. According to the Insight Volumes he wrote this in December of 518 BCE (within the 70th year of the 587 BCE destruction date). If he did not really mean that, why did he write it? Should we not stick to the obvious and plain meaning of scriptures?