Mobile: Tap on your profile picture in the top left to open your app settings. Tap 'Copy' to copy your Session ID and easily send it elsewhere. Tap 'Share' to directly share your ID to other apps or email.
You can also tap the QR code icon in the top right to open a QR code containing your Session ID. You can scan it or share it by tapping 'Share'
Desktop: Click your profile picture in the top left-hand corner. Click 'Copy' to copy your Session ID to your clipboard.
You can also click the QR code icon next to your profile picture to open a QR code containing your Session ID.
You can watch this video to learn more about Session IDs.