bitcoin duplication - Can Bitcoin transactions be double-spent?

How Does a Blockchain Prevent Double-Spending of

Bitcoin's blockchain prevents double-spending by using timestamps, proof that work was done, a network of nodes with copies of the blockchain, 

Crypto-Counterfeiting

Blockchain was supposed to solve the problem of asset duplication, referred to in blockchain circles as the double-spending problem, or in more recent incidents 

Token duplication

They store the original Bitcoin, providing in return its “digital copy” in another blockchain. In general, the scheme of work is as follows 

What happens if a transaction is duplicated across different

It doesn't matter if it's the same or a different block, it's still a double spend because both transactions spend the same coins.

How likely is it that Bitcoin wallet private keys are duplic

The possibility of duplication of Bitcoin wallet private keys is extremely low and almost negligible. Here are some relevant technical 

How Bitcoin Solves the Double Spend Problem

The Double Spend Problem describes the difficulty of controlling or preventing the duplication of digital content, especially with regards to digital money.