What they are really asking
This one sounds like a joke, but it's an honesty test. The interviewer is asking where your boss thinks you are right now. If you say "I told her I was sick," they learn that you lie to your employer when it's convenient, and they'll assume you'd do the same to them.
The good news is that you don't have to tell your current boss you're interviewing. Most people don't. You can take a vacation day, a personal day, a long lunch, or schedule the interview outside work hours. The answer they want is one that is true, discreet and respectful to your current employer.
A shape that works
Fact, respect, done. Say what you actually did in one sentence: you took a personal day, it's your day off, you're on your lunch break. If it helps, add one sentence showing you're being careful about your current job, like making sure your work is covered. Then stop. This is a short answer. A long explanation sounds like you're hiding something.
Model answers
Listen to how each answer is built, then make it yours.
Check yourself
Practice · 3 min
Say out loud what you would really do to attend an interview during work hours: a personal day, a day off, a lunch break. Write it as two or three true sentences, record them and time yourself. Twenty seconds is plenty for this one.
Your recording stays on this device. Nothing is uploaded.
Say it today
Use it once in a real conversation before tomorrow. Out loud counts, even to yourself.