In To Kill a Mockingbird, Mr. Underwood is "the sole owner, editor, and printer" of the town's newspaper, The Maycomb Tribune. Thus, the answer is "C." He normally spends his days firmly planted at his linotype, preparing every edition of the newspaper "out of his own head" with a jug of cherry wine at his side. Scout states that Mr. Underwood doesn't have to seek out the news because people willingly bring it to him.
Mr. Underwood's office (which doubles as his home) is situated on the northwest corner of the square, and he can see the "hideous" county jail by looking out of his upstairs window. On the night that Atticus has to face down the mob of men who have come to lynch Tom Robinson, Mr. Underwood leans a double-barreled shotgun out of his window, ready to come to the rescue if necessary. He ultimately proves to be a good ally and supporter for Atticus.
On a final note, the page numbers for this information vary by the edition of the book that you are referring to. In my digital edition of the book, the first mention of Mr. Underwood is on page 149.
Mr. Underwood ran the newspaper. Scout explains it on page 150. She says,
"Mr. Underwood not only ran The Maycomb Tribune office, he lived in it. That is, above it. He covered the courthouse and jailhouse news simply by looking out his upstairs window." (pg 150)
When Atticus is at the jailhouse defending Tom Robinson from the mob that had gathered, Mr Underwood was watching. The children arrived and Scout made the men feel guilty and dispersed them. She told Mr. Cunningham that Atticus was working on his entailment, and that Atticus said that they would get through this together. Mr. Cunningham cleared out the rest of the men. When they were gone, Mr. Underwood said he had Atticus covered with his double-barreled shotgun from the window of the Maycomb Tribune.