Possible Clues:

• Capital electoral system, unclear? Not very
• Where Mozart's 'Don Giovanni' premiered
• Capital of Puerto Rico's leaders with a visitor losing the way
• Capital's power remnant European Union rejected
• European capital with a medieval astronomical clock
• European capital known as the "City of a Hundred Spires"
• Czech city that's home to the Franz Kafka Museum
• City occupied by Soviet troops in 1968
• City occupied by Soviet Union troops in 1968
• Under pressure, debate moving queen up one space — capital!