My friend is a lawyer experienced in these matters.

1) My friend is a lawyer experienced in these matters. (without a comma)

2) My friend is a lawyer, experienced in these matters. (with a comma after "lawyer")

3) My friend is a lawyer, who is experienced in these matters. (with a comma after "lawyer")

Q1) Are they all correct?

4) "As it happened" reports an event whose occurrence was previously in doubt or not expected, often in contrast to what was expected.

Q2) What does the underlined part describe/modify in the previous sentence? Does it modify the verb "report"? Or does it modify the noun "an event"? Or the clause "whose occurrence was previously in doubt or not expected"?