Beijing Maliandao is a tea market. Many tea shops there. Find a shop looking nice. The owner will be very happy to introduce various kind of tea and teach you how to make tea. You can taste and buy some. I dont think it is possible to see how tea leaves are made in a workshop in Beijing. There is no tea plants here, if you mean by tea making process. If you live in China, you may arrange a tour to Hangzhou in Spring, March or April. Visit the tea garden, pick tea leaves and make tea. The famous tea produced there is Longjing (dragon well) tea.

very nice tea places there but i love the wanso tea shop the have fantastic tea and divine tea pots and tea sets made of porcelain:D