1. Take this medicine after 30 minutes after meals.

2. Take this medicine 30 minutes after meals.

(Which one is correct? Do you have other expressions?)

3. In the UK, what kinds of noblemen were there? For example,baron, knight, etc.(This is a question.)

#2 is good; #1 is very awkward.

3. http://en.wikipedia.org/wiki/British_nobility <~~You can see the list of titles in the box on the left.

1. Both sentences convey the same meaning, but there is a slight difference in phrasing.

The first sentence, "Take this medicine after 30 minutes after meals," could be rephrased as "Take this medicine 30 minutes after meals." The word "after" is used twice in the original sentence, which might sound a bit redundant. The corrected sentence eliminates the repetition and reads more naturally.

Other expressions you could use to convey the same meaning include:
- "Take this medicine half an hour after meals."
- "Take this medicine once 30 minutes have passed after meals."

2. Regarding your question about the UK noblemen, British nobility historically included various ranks and titles. Here are some examples of noblemen in the UK:

- Baron: A nobleman ranking above a knight and below a viscount. The title of baron is usually hereditary, and barons often held land given to them by the king.

- Knight: Originally, knights were mounted warriors of noble birth. Later, the title became more diverse and had various levels, such as knights bachelor, knight bannerets, and knights of the Garter.

- Viscount: This is an intermediate rank between a baron and an earl. Viscounts ranked below earls and above barons.

- Earl: An earl, also known as a count or a countess, is an aristocratic title ranking above a viscount and below a marquess.

- Marquess/Marquis: The title of marquess is higher in rank than an earl and below a duke. It is sometimes also spelled as marquis.

- Duke: The highest rank of nobility in the UK, below the royal family. Dukes are addressed as "Your Grace" and may hold significant power and influence.

These are just a few examples of the kinds of noblemen that existed historically in the UK. There were additional titles and ranks that varied in importance and privileges. British nobility has a complex and rich history, with changes occurring over time.