Geoff Fennell is a reporter.
He works for an unnamed British newspaper which he describes as "one of the most important newspapers of my country" and has for quite a few years by the time we come across him in the first recorded adventure. He is not being cagey when he omits the name of the publication; he just knows based on that long of employment that who he works for is never the story and Fennell is always and ever about the story.
Fennell is part of that organization's Foreign News Department and writes a regular, though not necessarily daily, column for it under the title of "Man on the Spot". The "spot" invariably is wherever his editor, or sometimes himself, feels is the most interesting at the time. Based on the fact that he muses at one point that his professional travels had taken him to "most of the big cities of the world", it is a constantly changing spot; based on Fennell's attitude towards always being on the more, he would have it no other way.
His membership in this compendium comes from the fact that those spots he heads to invariably present matters of international intrigue which is of a lot of interest to the readership of his employers (i.e., they help sell a lot of copies of the paper and keep the subscribers coming back for more). While we do not know what his age is - he definitely comes across as being at least in his mid-to-late-30s - we do know that he has seen quite a bit of action.
The most interesting aspect of Fennell is his use of language when he interviews people - and no matter what the situation is or who is he conversing with, it is subtly apparent that Fennell considers very conversation as an interview. While he does not speak particularly slowly, he does choose his words very carefully. What makes that interesting is that invariably the other party in the exchange so often either deliberately or intentionally 'misinterprets' what he says and tries to steer the conversation elsewhere. Fennell is very, very good at patiently and calmly correcting the mistake and bringing the topic back to where it was. This does tend to be very annoying to people with something they wish to hide.