The most commonly used airports for such a trip are:

• Frankfurt International Airport (FRA)
• Dusseldorf International Airport (DUS)

Both are served by US-American Airlines from the US. There are also non-stop flights to Frankfurt, which you may want to prefer.

Airport Cologne-Bonn (CGN) is actually closer, but less commonly used for such trips and in my experience typically more expensive.

The most commonly used airports for such a trip are:

• Frankfurt International Airport (FRA)
• Dusseldorf International Airport (DUS)

Both are served by US-American Airlines from the US. There are also non-stop flights to Frankfurt, which you may want to prefer.

Airport Cologne-Bonn (CGN) is actually closer, but less commonly used for such trips. Trying to use it for a transatlantic trip typically leads to higher airfares in my experience.