She could be terrified at first. After all, Klaus is a very powerful and dangerous vampire. But Elena is also a strong - willed character. So she might quickly gather her courage and start looking for ways to escape.
Elena would likely be angry. She has her own agency and doesn't like being controlled. If Stefan kidnapped her, she would fight back. She might use her knowledge of the supernatural world and her relationships with other characters to try to escape. For example, she could try to call out to Damon telepathically if they have some sort of connection in the story.
She's likely to be defiant at first. Elena has a strong will, so she would probably resist Klaus's orders and try to escape.
Elena would probably be terrified at first. She might try to fight back or escape immediately. After all, Kai has a reputation for being dangerous.
Elena would probably be terrified at first. She's a human in a world full of powerful supernatural beings. Being kidnapped by Damon would mean she's in a very vulnerable position. She might initially try to fight back or escape, using any opportunity that presents itself.
Well, one possibility is that Elena's friends would immediately start a search party. Damon, for instance, would be furious and stop at nothing to find her. He might enlist the help of Stefan and Bonnie. They could use Bonnie's magic to try and track Klaus' whereabouts.
Elena might be heartbroken. She probably expected Damon to always be there for her, so his choice of Bonnie would come as a shock.
Stefan would be extremely worried and angry. As Elena's other love interest, he has a deep connection with her. He would immediately start looking for her, using all his vampire skills and resources. He would probably suspect Damon right away, given their history of rivalry over Elena.
The Salvatore brothers, Stefan and Damon, are the most likely candidates. They both have a strong connection to Elena and would stop at nothing to rescue her. Stefan's sense of chivalry and Damon's fierce protectiveness would drive them to track down Katherine and get Elena back.
Well, it can have a huge impact. For instance, if Klaus saves Elena from a life - threatening situation, Elena might start to feel a sense of gratitude towards him. This could make her more open to his presence and less hostile. It could be the start of a strange friendship or an even more complex relationship where she's conflicted between her loyalty to her friends and this new - found connection with Klaus.
One great Klaus and Elena fanfiction is 'The Bond Beyond Blood'. It explores a unique relationship between them where they have to team up against a common enemy. The story is filled with intense emotions and some great character development for both of them.