In the film "Don't Look Back", what is written on the last card held
up by Bob Dylan?

Thanks for the interesting question!

I assume you are referring to the scene in the beginning of the
documentary when Dylan is holding up cards containing text from
"Subterranean Homesick Blues."  The last card contains the text
"WHAT??"

An interesting article on the documentary, as well as a screenshot of
Dylan holding one of the cards, can be found at:

Bright Lights Film Journal
http://www.brightlightsfilm.com/33/bobdylan.html

You may purchase a DVD version of the documentary at:

Amazon.com
http://www.amazon.com/exec/obidos/tg/detail/-/B000035P7X/qid=1058371603/sr=8-1/ref=sr_8_1/103-5986219-0468626?v=glance&s=dvd&n=507846

The lyrics to "Subterranean Homesick Blues" can be found at:

Bob Dylan.com
http://www.bobdylan.com/songs/subterranean.html

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Thanks,

-Blinkwilliams

Absolutely great answer, exactly what I was looking for and prompt. Many thanks!