You will need to wait a while in game for the zone to actually populate enough.

Specialized Zoning: These require specialized zoning, create a district over the appropriate base zone type then switch it to the appropriate type.

Grand Library: Requires 7 Universities for 10 weeks.

High Interest Tower: Requires you to have $2,000 in debt (Not technically purchasing, but just take out the largest loan, then pay it back.).(Build a bunch of water towers in the boonies.) Servicing Services Office: Requires 300 city service buildings.Theater of Wonders: Requires 3 Universities.Sea and Sky Scraper: Requires Cargo Harbor and Passenger Harbor.Zoo: Construct Fishing Pier and Riding Stable.Luxury Hotel: Construct International Airport.Just build whatever is needed, make sure it has power/water/etc and that it registers the building as complete before going back to your previous save files. Purchasing: For these you just need to buy certain things and place them in your city, super easy if you have enough money (which you should).These will either mess up your city or waste money, so save your game, accomplish a few, then reload, the buildings will stay unlocked. Eiffel Tower: 30,000 squares of industrial zone built.Statue of Industry: Requires 10,000 squares of industrial zone.Arc de Triomphe: 15,000 children in elementary schools.MAM Modern Art Museum: Requires 50% of population highly educated.Aquarium: Requires 5,000 children in elementary schools.Official Park: Requires 10,000 squares of office zone.Business Park: Requires 20,000 squares of commercial zone.Colossal Order Offices: Requires education at $20,000/week for 10 weeks.Tax Office: Requires electricity production of 1,000 MW.Friendly Neighborhood Park: Requires 10,000 squares of residential zone.Transport Tower: Requires 1,000 weekly passengers.Grand Central Terminal: Fill 7 instances of Cemetery.Plaza of the Dead: Requires 3 full Cemeteries.Brandenburg Gate: 10,000 full lifespans lived in the city.Science Center: Requires 5,000 full lifespans lived in the city.Fountain of Life and Death: Requires one full lifetime spent in a city.Statue of Liberty: City produces a total of 5,000 units of goods.Stadium: City produces a total of 1,000 units of goods.These buildings should all be completed already from what you have done so far

Cities skyline unlimited money