What is the accented syllable in surface

It refers to the stressed syllable in a structure. You should also consider that:

- a syllable is a pronunciation unit having one vowel sound. For example: dog, blue.  

-the stress is the emphasis you give to a syllable (making it longer and louder). For example in the word “banana” the second syllable is stressed.

In the following structures, you can see the accented syllable in bold and underlined:

-intonation is another aspect you should consider when stress is applied not only in isolated words but in a whole structure:  it is the rising or falling sound of the voice when speaking.

Here you have more examples: (the underlined part is the stressed one)

-I´m Japanese.

-Are you lonely in your house?

-I enjoy dancing!

1- cleans/ tidies up

2- were

3-would be

4- had known

5-takes

6-must be/ have to be/should be