1. He met the boy here.

Question

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Q1: Does 'the boy' modify 'met' or 'the boy'?
Q2: Is 'here' an adverb or an adjective?
Q3: Did he meet the boy here for the first time? Or did he meet the boy here whom he knew before?

Answer 1

Q1 -- "the boy" is a noun and its article; it doesn't modify anything.

Q2 -- "here" is an adverb.
"Adverbs answer one of these four questions: How? When? Where? and Why?" http://www.chompchomp.com/terms/adverb.htm

Q3 -- There's no way to answer this without the rest of the paragraph to understand the context.

Answer 2

1. He met the boy here.
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Q1: Does 'here' modify 'met' or 'the boy'?
Q2: Is 'here' an adverb or an adjective?
Q3: Did he meet the boy here for the first time? Or did he meet the boy here whom he knew before?

Answer 3

Q1 and Q2 -- "here" is an adverb. It tells where.
"Adverbs answer one of these four questions: How? When? Where? and Why?" http://www.chompchomp.com/terms/adverb.htm

Q3 -- There's no way to answer this without the rest of the paragraph to understand the context.

Answer 4

Thank you very much for your help.
What about the following?
1. Look at the boy there.
2. He knows the boy there.
3. He saw the boy there.

Does 'there' modify 'the verb' or ' the noun phrase'?

Answer 5

I know you want "there" to be an adjective modifying "boy" even though the standard use for "there" is as an adverb. It tells where.

https://www.merriam-webster.com/dictionary/there
Scroll down to the section there adjective
Notice that it says that using "there" like this is for emphasis or is non-standard. In your sentences, the word seems to be used for emphasis.