How long to arrive at airport before continental/international flight ?
 

When we fly direct from Europe to the US (or the other way around), we allow three hours at the airport. This time we’re flying from Prague to Frankfurt, connecting at Frankfurt to Los Angeles, on Lufthansa - so the original flight is continental (and within the Schengen zone). Is two hours sufficient, or should we arrive at the airport in Prague three hours ahead?

Thank you in advance for your advice and experience.

Two hours is easily enough. But do allow time at Frankfurt for going through passport control to leave Schengen and another bout of security.
I assume it is all on one ticket.

Thank you! Yes, on one through ticket. I think we have three hours in FRA.