I joined a company who works in fintech technologies and I have almost zero knowledge of the field... Where should I begin?

Learn basic accounting. Then advanced accounting. Webservices for integration with partners, owasp for web security, cryptography for data security, iso8583 for bank and switch integrations,.. most secured protocols (ssl,ipsec,vpn). Learn to increase your patience and endurance as every mistake is a cruicial one since money is involved... cryptocurrency is a plus but not required.. cheers! Wishing you all the best!

Basic stockmarket books, depends on what area your company is Aimed at.

But I would suggest:

The Intelligent Investor or any of these 20: https://stocktrader.com/investing-b...

get an overview/benchmark on how shitty or good the competitors products are. You'll be amazed on how little they know and feel good about it. 😉