You don't need to apply for a transit G visa between Beijing and Shanghai, the China L Visa is sufficent for you to travel Shanghai and Beijing. I advice you to read China Tours(https://www.travelchinaguide.com/tour/default.htm) to see the wonderful itineraries of Shanghai and Beijing.

You need no other visa to travel in mainland China. Unless you have a multi entry visa you will not be able to go to Hong Kong, (you can go but can't get back to mainland.) Air China is a good airline and is part of the Star Alliance. China Eastern I have used for domestic flights within China but not internationally. Another good airline is ANA, it is Japanese. You have a lay over in Tokyo, but the airline is great. There are many domestic airlines once you get there. While there use 9588 (keyword...Google) to book inexpensively and get an idea of the many options you have. A good travel agency. I used them for 8 years while living in China.

hello i am a nigeria live in ghana now i want to visit china for business i have my passport how can i get the visa? i also have a friend for business over in china did i need to pay for hotel aslo?
pls i need ur quick reply

Sorry, Mr.Oliver, I thinks you post in a wrong place by following others, i am wondering if you can see the reply in time.. For a business visa to China, you need to provide:
1.One completed visa application form with a recently taken passport photo stuck on it; all the items on the application form should be completed neatly with genuine information; false or incomplete information and illegible characters may lead to refusal of a visa.
2.Visa Notification Form issued by an authorized unit in China (Visa notification refers to the form of visa notification issued by the Chinese government departments, companies and social organizations authorized by the Chinese Foreign Ministry. The Chinese company who gives invitation knows how to get this form).
3.One formal introduction letter from the your company to tell identity， the purpose of visit to China, and supposed duration of stay in China.
4.The original and one photocopy of the your ID card. (The original will be returned at the interviews).
5.The original and one photocopy of your certificate of incorporation. (The original will be returned at the interviews).
6.Hotel reservation in China and round-trip ticket between Nigeria and China.
7. Recent bank statement of account.
8.Photocopy of your passport data page and all the Chinese visas if any.