Dracula, what is "the less"?

I suppose one could allege poor writing by Stoker. It means tta not only did he know what to do, but as the howling of the wolves came closer, he knew even less what to do--i suppose Stoker was suggesting that he began to panic.

I doubt his English would be so poor.
Old-fashioned English sometimes confuses modern readers.

Means:

I did not know what to do. I knew even less what to do as the howling of the wolves grew closer.

Old-fashioned. Not bad English.

The less, the more...

We use "the" with a comparator (e.g. more, less, fewer, larger, smaller, etc) when we wish to convey the idea that two things vary together or are linked.

I was not feeling brave, the less as the lion grew nearer.

I grew hungry as evening approached, the more because my lunch had been small.

The more the building shook, the more we held on.

The more the wave rose, the faster we ran.

The more we saw, the less we could believe.

The more we looked, the fewer things we found to retrieve.

The more you dump materials in this store, the less you leave vacant space available for useful things to be kept.