Might it be either of these, from www.cyberhymnal.org
?
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Watchmen on the walls of Zion, what, O tell us, of the night?
http://www.cyberhymnal.org/htm/w/a/t/watchwoz.htm

Watchman, tell us of the night
http://www.cyberhymnal.org/htm/w/a/watchman.htm

If anyone knows a song about a "watchman on the wall", or asking "watchman what of the night", I would greatly appreciate it. I need a song for campmeeting in two weeks. Please help!!!!