Where can I find information about the protocol for transaction schema?
I found this https://github.com/neo-project/neo/wiki/Network-Protocol document but it is unclear how to build tx.
I wrote a decent guide here, it is a bit old, but will help you get started
https://steemit.com/neo/@saltyskip/creating-a-light-client-for-neo-a-blockchain-developer-s-gateway-drug
https://github.com/CityOfZion/neo-swift/blob/master/NeoSwift/Account.swift#L115
Anyway, I will need to use https://github.com/CityOfZion/neon-wallet-db or is there another way to get UTXO for an address?
Yes you need some sort of database that keeps tracks of all the associated UTXO's for a given address. I think neon-wallet-db might be deprecated, but I am not sure
That is sad, but thanks for reply
Most helpful comment
I wrote a decent guide here, it is a bit old, but will help you get started
https://steemit.com/neo/@saltyskip/creating-a-light-client-for-neo-a-blockchain-developer-s-gateway-drug
https://github.com/CityOfZion/neo-swift/blob/master/NeoSwift/Account.swift#L115