I hate it when an SP asks that.
I now just answer with a shocked expression: "Never - I'm still a virgin so be gentle with me!" Then, when I step out of the shower butt naked, I ask them "Am I your first too?".
I no longer mind them asking "What do you do for a living?", "Are you married?", "Any kids?" etc... as it gives me the chance to live in my own little fantasy world. Lots of guys aren't prepared for these questions and blurt out the truth so its best to plan answers in advance. For example, here's some stock answers I've used on occasion:
Question: What do you do for a living?
Answer: I live on an Island, dress in white suits and cater to people's fantasies, all the while ably assisted by a vertically challenged little guy who speaks English with a French accent and a bad lisp and says "Da Plane...Da Plane..."
Question: Are you married?
Answer: "I am a member of a breakaway Mormon sect that still believes in multiple wives. I only have 6 wives at present and they are very jealous so I only get to spend 1 night a week with each of them. This means I have one day off, but I crave sex 7 days/week. Guess which day this is? Hmm... nice body. Interested in getting married and helping the others back on the farm?"
Question: Any kids?
[I scrunch up eyes and pretend to be counting]. "Hmmm... 3 from wife 1; 1 from wife 2; 4 from wife 3; 2 from wife 4; 8 from wife 5 (call her "Bunny"...); ..... And I'm so virile there must be lots of other kids out there that I don't know about yet...."
And, of course, there's answers we want to hear from SPs to the same questions, such as:
Question: Are you married?
Answer: "No. I've never yet found a man who could satisfy me but thank goodness you've finally arrived. I heard so much about your sexual prowess from other SPs that the session is free.... no, wait, you're so good I insist you let me pay you."
Question: Do you have kids?
Answer: "No. Oh, that's not a caesarian scar. It's from having my tonsils removed when I was younger. Ah...no...that's not right. It's an appendix scar. Yeah right. That's it. Appendix."
Take everything you hear with a grain of salt. Most SPs want their private life kept private so be understanding if they give you a different story each time you see them. They should do likewise.
There's no shortage of topics to discuss that don't requiring divulging personal information. There's always the weather, the bitch of a time you had parking near her place, what's on at the Ballet (oops, that slipped out

meant to say ..... hockey game... err.. football game... monster truck rally... you know - manly stuff...).
Once you're both butt naked, conversation is easier. Hell, you can spend half an hour alone flirting with her as she compliments that monster schlong between your legs and builds your ego by saying you're much too big for her and she's never experienced someone that big! Live with the fantasy, and don't question the fact she reached for the extra small condoms and left the extra large one on the bedside table. Once the condom is on and you're pumping away, conversation is irrelevant because you can't be heard over her screams of ecstasy as you expertly bring her to orgasm with the first few strokes.
Oops... sorry. As I said, in this industry it's hard to separate fact from fiction, fantasy from reality.
In all seriousness, I rarely tell SPs personal information about myself unless I've become a "regular" and know that she is discrete and can be trusted. Some SPs even share their real names and other personal details with me, which of course I hold in strictest confidence. Sometimes this is purely accidental such as the time an SP was proud to tell me she had achieved a certain honour and then took me by the hand to show me the certificate on her wall in another room which she received. She burst out laughing when she realized she was showing it to me with her full name prominently displayed! Fortunately, my mind is like a sieve when all the blood is in the little head.
Don't ever ask an SP for private information about herself. If she wants to share any personal information with you, leave it to her to volunteer it. Hopefully, she will be considerate enough to treat you the same way. If not, print out the above answers.