'What ho!' of Bertie Wooster

It's a Shakespearean reference. Try googling "what ho Othello" or "what ho apothecary".

I think it's probably intended to allude to Bertie Wooster's (presumably expensive) education and illustrate his flippant nature.

In my opinion this is nautical in nature, deriving from "Land ho!", the traditional lookout's joyful cry on sighting land. Bertie usually uses this in greeting, and the meaning is roughly "What's up?", or "What's going on?" For a sailor, land is what is going on; for Bertie he doesn't know and he's asking.

Isn't 'ho' in this case from the middle english - meaning 'who'?

I dont have reputation to comment :( However, the Daily Mail is an English tabloid 'newspaper' which should not be regarded as a reliable source.

I grew up Wednesfield, Staffordshire (near Wolverhampton, England) in the 1950s and 60s where "What ho" was a very common greeting between young working class lads although it was usually pronounced as "Worro" (often followed by "our kid"). It certainly wasn't trying to be pretentiously Shakepearean! Much more likely the utterance had simply remained in usage from pre-Shakespearean times. I've often wondered if "what ho" is itself a shortening/corruption of "What, who's this?", or if "ho" is related to "hove" (as in the nautical "hove into view").

Other common greetings were "Watcha" (l suppose short for "what are you doing/up to") and "Alright?" Although we sometimes said "Hullo" we never said "Hi" or "Hey". Grown ups would often say "how do you do?" shortened to "how do?".