What if I fall asleep during the khutbah?

Your Jumu'ah is still valid, but try not to make a habit of it. Nodding off is human, and you won't be punished for something you didn't choose. If you feel sleepy, the sunnah is to move to another spot. If you fall into a deep sleep, renew your wudu before the prayer.

Is my Friday prayer still valid?

Yes. Listening to the khutbah is required or strongly emphasized, but dozing off does not cancel your Jumu'ah as long as you join the prayer itself with the imam. Allah does not hold us to account for things beyond our control. Still, the khutbah is the main reminder of the week, and Allah tells believers to hurry to it:

يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ إِذَا نُودِىَ لِلصَّلَوٰةِ مِن يَوْمِ ٱلْجُمُعَةِ فَٱسْعَوْا۟ إِلَىٰ ذِكْرِ ٱللَّهِ وَذَرُوا۟ ٱلْبَيْعَ "O you who have believed, when [the adhan] is called for the prayer on the day of Jumu'ah, then proceed to the remembrance of Allah and leave trade." Quran 62:9

The sunnah: change your seat

The Prophet ﷺ said that if one of you feels drowsy on Friday, he should move from his place to another one (Jami' at-Tirmidhi 526). Shifting your position wakes up your body and mind. You can do it quietly: slide to a spot nearby without stepping over people or talking.

Do I need to redo wudu?

Light dozing while sitting firmly: most scholars say your wudu stays. The Companions used to nod off while waiting for prayer and then pray without renewing wudu (Sahih Muslim 376).
Deep sleep, where you lose awareness, slump or lie down: renew your wudu before the prayer starts.
If you're unsure, renewing it is the safe choice. See Does sleeping break wudu?

How to stay awake

Sleep early on Thursday night and have a light lunch before Jumu'ah.
Sit up straight rather than leaning on a wall or pillar.
Sit closer to the imam; it's easier to stay focused.
Avoid your phone, which drains attention fast. See Can I use my phone during the Friday sermon?
Don't wake others by talking. The Prophet ﷺ said that even telling someone "be quiet" during the khutbah counts as idle talk (Sahih al-Bukhari 934). A gentle tap is enough.

If you don't understand the language

Many converts get sleepy because the khutbah is in Arabic or another language they don't follow. Try a mosque that gives the sermon in English, or read a translated summary beforehand. See Can the Friday khutbah be in English?

Key points

Dozing off doesn't cancel your Jumu'ah.
If drowsy, quietly move to another spot.
Deep sleep means renewing wudu before the prayer.
Rest well the night before and sit closer to the imam.

Tip: Bring a small notebook and jot down one point from each khutbah. Having something to listen for keeps you awake, and you'll leave with a lesson to act on that week.