What is the Italian equivalent of the expression: to know something
"like the back of my hand?"   Someone in a chat room said, "come la
tasca mia" - like the inside of my pocket- but I cannot confirm this. 
Since slang is regional, I am interested in the area around Naples and
the Amalfi Coast if you have a choice.  Please provide THE EXPRESSION
AS WELL AS THE LITERAL TRANSLATION.  Thanks.

Hi Dave

You've probably already found that "come la tasca mia" doesn't show up
anywhere in a google search:
://www.google.co.uk/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=%22come+la+tasca+mia%22&sa=N&tab=gw

The correct idiom is not too far off. It's "come le mie tasche", which
means "like my pockets".
(Come = like, le = the, mie = my, tasche = pockets)

You can check this on the WordReference site:

"Conosco Roma come le mie tasche, I know Rome like the back of my
hand"
http://wordreference.com/it/en/translation.asp?iten=tasche

You may also say "come il palmo della mia mano ", meaning "like the
palm of my hand", but this is more unusual.

"I know Naples like the [back] of my hand, conosco Napoli come il
palmo della mia mano {or} come le mie tasche"
http://wordreference.com/it/translation.asp?enit=back


* * * *


Although the WordReference examples are both about cities, the phrase
is also used in other situations. One way of seeing how Italians use
the idiom is to check its frequency and context on a number of
websites.

"Come le mie tasche" appears nearly 400 times in google search
results:
://www.google.co.uk/search?q=%22come+le+mie+tasche%22&ie=UTF-8&oe=UTF-8&hl=en&btnG=Google+Search&meta=

More often than not it is with the word "conosco" (I know):
://www.google.co.uk/search?q=conosco+%22come+le+mie+tasche%22&hl=en&lr=&ie=UTF-8&oe=UTF-8&start=70&sa=N


Here a coach knows a football player "like my pockets":

"Zidane. Lo conosco come le mie tasche"
http://lanazione.quotidiano.net/2003/07/14/pages/artI4546474.html

In this resume/CV someone says he knows English "like my pockets" as
well as having qualifications in law and computer skills:

"Sono laureato in giurisprudenza, ho fatto un corso di
specializzazione su Windows 2000 [...], conosco l'inglese come le mie
tasche . . ."
http://www.padovanet.it/infogiovani/post.asp?topic=120&forum=14


Searching google groups, you'll find "come le mie tasche" 800 times:
http://groups.google.co.uk/groups?hl=en&ie=UTF-8&oe=UTF-8&q=conosco+%22come+le+mie+tasche%22&meta=&sa=N&tab=wg


* * * *


"Come il palmo della mia mano" is less common:
://www.google.co.uk/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22come+il+palmo+della+mia+mano+%22&btnG=Google+Search&meta=

It is very little used in newgroup messages:
://www.google.co.uk/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22come+il+palmo+della+mia+mano+%22&btnG=Google+Search&meta=


Stick to "come le mie tasche" and your Italian should sound idiomatic!

Please feel free to ask if you need anything clarified and I'll be
happy to help.


Best Wishes - Leli


Search strategy:

The searches I used were based on my knowledge of Italian, and are
outlined in the text of the answer.

Wonderful job; I am completely satisfied.  Work like this is why tips were invented.

Thank-you very much for your kind, appreciative message and generous tip. 
It's great to know the answer was what you wanted.

Leli