Does “little did he know” mean he "knew nothing at all"?

Solution 1:

Little when used as an adverb can mean:

not at all (used before a verb): He little knows what awaits him.

This is the same usage as in "little did he know", which hence means "he knew nothing about it".

As per Dan's comment on the question:

'Little did he/she know...' is often used to highlight how someone who thinks they are in control/well informed, actually, is not.

Solution 2:

"Little did he know..." means that "he did not know about ..."

For example:

Little does Luke know that the GALACTIC EMPIRE has secretly begun construction …

This would mean that Luke did not know that "the GALACTIC EMPIRE has secretly begun construction"

It can be re-written as:

Luke does not know that the GALACTIC EMPIRE has secretly begun construction

(though the first one does sound better)