Hi and welcome to iLounge.
The short answer is that there's no direct way to do this. iTunes will sync your Yahoo address book, but not the calendar.
That having been said, if you can find something that will sync your Yahoo calendar with Outlook as an intermediate step, you can transfer it from there to your iPod. Further, if you're using an iPod classic or iPod nano and can export your Yahoo calendar in an iCalendar/vCalendar format, there are methods for transferring this to your iPod as well.