Please help! 144 hour transit query. MANC- PVG -HKG- PVG- MANC

Sophie, your entire itinerary is definitely and undeniably eligible for 144 hour visa free transit in Shanghai twice and you do not need any kind of visa. Your itinerary will not be counted as a return trip, but as two trips:

Manchester - Shanghai - Hong Kong
Hong Kong - Shanghai - Manchester

In the eyes and based on 144 hour visa free transit rules, one visa free transit journey ends in country A (UK in your case), travels through country B (mainland China in your case) and terminates when it reaches country C (Hong Kong acts as a country for this rule regardless of the fact that it is an integral part of the country of China). When it has reached country C, the journey is over and you can start a new one. So, you should not be confused, but quite contrary, relaxed and enjoy your upcoming journey.

If you plan to stay at your friend in Shanghai instead of a hotel, you can do that, just have her/his full identity, address and a phone number ready because you will have to supply the immigration officials with these details. Also, you will have to register at the closest PBS within 24 hours upon your arrival, accompanied with your friend. Just a formality, but it has to be done. If you plan to stay at the hotel, you do not perform any formality.