what responsibilities does a stockier at Walmart have?
Walmart is one of the world's most valuable companies in the United States. I believe that a stock person would be responsible for obviously stocking, assisting with inventory and customer service. 
what do you mean by helping with customer service?
At Walmart, I believe a stock person could assist in customer service by providing service to the customer during the process of a purchase - such as locating a particular product.
Is this done with the use of technology or by the stocker's knowledge of the store layout?
I believe it would involve both. I believe a stocker's knowledge as well as the use of technology would work together to provide the ultimate customer service for a potential purchaser.
What kind of technology does the stocker have access to that would help the customer?
Stock persons would have access to a computer database which would provide inventory levels as well as store locations for a particular product.
But, how is this achieved? Locator gun, cpu, etc. What specifically do they use?