Harry might initially be very confused. He trusts Albus to some extent, so he would be bewildered as to why this is happening. He could try to reason with Albus at first.
At first, Harry would likely be shocked and feel betrayed. But then, he would start to look for ways to escape. He might use his own magic skills, which he has learned over the years, to try and break free from whatever bindings or location Albus has him in. He would also be constantly thinking about his friends and how they might be looking for him. He would probably be angry too, especially if Albus doesn't give him a clear reason for the kidnapping.
Well, at first, Harry could be alarmed. He has a protective nature, especially when it comes to Albus. If he catches them in a situation where they seem to be in over their heads, he might immediately step in to rescue them if necessary. He would then likely express his disappointment in their actions. However, if he realizes that their intentions were good, like trying to help a fellow student who was being bullied by using some unorthodox magic, he might be more understanding. He could guide them on how to use their skills and ideas in a more proper and approved way at Hogwarts.
At first, Harry may be in shock. He's been taken by someone he respects and looks up to. As he comes to terms with his situation, he might try to reason with Dumbledore. If that doesn't work, he could start to plan an escape, using his wits and the magic he knows. He might also feel angry that Dumbledore is treating him this way when he's always been on Harry's side, or at least that's what Harry thought.
Harry's reaction could be a mix of fear and defiance. He's faced Voldemort multiple times, so he won't be completely helpless. He may try to understand Severus' psyche, remembering that Severus has always had a somewhat ambiguous relationship with him. He might try to appeal to Severus' better nature if he believes there is one. Harry would also be thinking about how this situation affects the overall fight against the Dark Arts and Voldemort. He might see it as a setback or an opportunity, depending on how he can turn the situation around.
At the beginning, Harry would be frightened. He's in an unknown place with Loki, who is known for his trickery. But Harry is no pushover. He would quickly gather his courage. He would remember all the times he's faced danger at Hogwarts. He might try to communicate with Loki to understand his motives. If Loki reveals that he wants to use Harry's magic for something, Harry would try to find a way to outsmart Loki. He could pretend to cooperate while actually looking for a weakness in Loki's plan. Harry would also be thinking about his friends at Hogwarts and how he needs to get back to them, which would give him extra motivation to fight back against Loki.
Harry might be initially angry. After all, he's been hurt. But he could also be a bit confused, especially if he thought Draco didn't mean to do it. In some cases, he might just walk away to cool off and think about what happened.
Harry might be initially shocked and embarrassed. A Howler is a very public form of scolding, and in front of all his friends and classmates, it would be a humiliating experience for him.
It could be a complex relationship. Maybe Albus has high expectations for Harry, which puts a bit of pressure on him. Harry, on the other hand, might feel that he has to constantly prove himself. However, there would also be a deep bond of family love. Albus would be protective of Harry, and Harry would feel a sense of security in his grandfather's presence.
Harry's own difficult experiences growing up, like being an orphan and facing Voldemort, make him empathetic towards Albus. He knows what it's like to feel alone and scared, so when Albus is going through tough times, Harry can draw on those feelings. For example, if Albus is being bullied, Harry can relate to that sense of being targeted and uses his own strength to encourage Albus to stand up for himself.
Harry may also feel a sense of adventure. Despite the situation, he's used to facing strange and dangerous things. He might start to think about how he can use this situation to his advantage, like finding out more about his parents or the secrets of the wizarding world that Sirius might know. He could be a bit excited as well as scared. For example, he might be thinking that this could be a chance to get away from the Dursleys for good.
Harry could initially be in shock. He's always counted on Hermione, so her abandonment would be a huge blow. He might feel a sense of betrayal and confusion.