Hey there, Susan, and welcome to planDisney!
Looking at my own
theme park tickets for an upcoming park visit, the easiest way to find your expiration date is in the confirmation email you received when you purchased them. If you search "Disneyland Confirmation" in your inbox, then you should see an email with the subject line "Disneyland Confirmation (#DDXXXXXXXXXXXXXXXXXX)" where the X's will be a unique number that makes up your ticket ID. If you scroll down in this email, you'll see a paragraph header that will tell you their expiration date.
If they are multi-day tickets that you purchased within the last year, then in all likelihood they will be good until January 12, 2025, if they have not been used yet. Once you used your multi-day tickets for at least one scan into the parks, though, they
expire within 13 days of first use.
Thankfully, theme park tickets have a very long time before they expire, but even if they do expire before you're able to visit the parks, you're still able to apply the amount paid to purchase new tickets!
If you don't have access to the email inbox or can't find your confirmation email, then your next best bet would be to
call a Cast Member at the Tickets line. They'll be able to take your ticket information and see exactly how long you have before they expire.
I hope that helps, Susan! Thanks again for your question and I hope you enjoy your visit to the Disneyland Resort.
Have a Magical Day,
Greg