How can the government discover I own BTC, let's say I'm from Venezuela where crypto is banned, what they can do to discover and arrest me?
You should avoid reusing addresses. You should also be careful to use coin control: remember that signing transactions with outputs from multiple addresses associates all those addresses together.
You should always use IP address obfuscation when broadcasting transactions to the network. You can push raw transactions over TOR using a push service like
https://blockchain.info/pushtx or you can connect to the network through a good VPN.
Bitcoin transactions are anonymous. As long as you don't reveal your identity, no one know you are a bitcoin holder.
For this purpose you have to buy bitcoin peer to peer from a person you trust. Never use exchanges that force you to verify your identity.
Bitcoin transactions
are not anonymous. They are pseudonymous. Even if you never fully verify your identity with an exchange, things like IP addresses, cookies and PII like physical addresses (e.g. if you've bought an Amazon gift card with BTC and had something shipped to your home) can be used to identify you. Lots of PII gets leaked when dealing with third parties via web browser. And if blockchain analysis companies (working with governments) can identify one or two of your used addresses,
clustering techniques may allow them to map much of your transaction history.
Be careful out there!
Yes, you are right. It is really hard to avoid tracking. So, Using VPN is the only secure way to bitcoin transaction. Otherwise there is always chance to be caught.
Also have to be careful about any transaction made with unknown person in your country. If he is your enemy, he may revel your identity.
This awareness is for bitcoin banned country. Also it's good to be precocious.