In short, the topic-comment structure puts the topic you want to focus on in the beginning of a sentence, optionally followed by a comma, and the comment you want to make about the topic right after.
As Dejavision has mentioned, in all of your examples, the topic can be the object. (see note below) Thus, moving the object to the beginning would change the structure to topic-comment.
- This trick does not always apply. The topic can surely be a subject as well.
Consider the following example:
As for this pen, the color is good-looking.
這隻筆 is both the subject and the topic.
- Depending on the context, the same sentence may have more than one potential topic.
Consider the following example with possible context in parentheses:
(I know that everyone likes going to the States.) As for Japan, do all Swedish like going there?
(I know that many Asians like going to Japan.) As for Swedish, do all of them like going to Japan?
The two questions have different topics, thus different context, but are asking the same thing.