You can do that with a script, here's mine. It reminds me every 15 minutes. It speaks it via speaker, then captures it and logs it and time.
#/bin/bash
while sleep 900; do
DATE=`date`
echo "Hello, what are you doing?" | espeak
DOING=`zenity -entry --text="what are you doing?"`
echo $DATE, $DOING >> ~/data/doing.txt
done