Did you try the options in:
File Manager PCManFM > Edit > Preferences > Volume Management > Auto-mount
Unlike all previous versions, 7.6 doesn't automatically mount CDs. I have to type "mount /media/sr0".
Did you try the options in:
File Manager PCManFM > Edit > Preferences > Volume Management > Auto-mount
That doesn't help.
Ok, found the problem. You have to add kernel option:
block.events_dfl_poll_msecs=1000
Looks like a strange command to me but if it works ...
Looks to me like more Linux gibberish. Sure, Linux experts enjoy saying to noobs "you just have to add a kernel option". It certainly demonstrates their superiority and better understanding. But many average users have no idea exactly how you "add a kernel option". It isn't hard to understand why Linux is still marginalized on the desktop.
---
Verifying of md5 checksum and burning a CD at slow speed are important.
At least it's an easy fix, just add it to syslinux.cfg (assuming your knoppix is on a USB stick).
My Knoppix 7.7.0 is a LiveUSB on a Dell Inspiron which has a r/w cd/dvd drive in it.
This implies legacy boot and a remote possibility of systemd messing with things.
I was surprised that cds were not always being recognized, along with other media.
However, I finally noted that, for my set-up anyway, a cd physically in place
in the cd drive reader during boot will be recognized, whereas a cd added after boot
will not be recognized.
So, one work-around for Knoppix 7.7.0 LiveUSB legacy boot users is simply just to
re-boot with the cd in place. I would not be surprised that this problem and work-
around might apply to earlier Knoppix LiveUSBs as well, but I haven't checked this out.

Novell SUSE Linux Enterprise Server 9, Linux Professional 8.2 / 9.1 — 3 DVD Set
$58.00
Microsoft SQL Server 2019 Enterprise 40 Core Unlimited CAL Retail License FPP
$299.00
Ubuntu Server 26.04.1 LTS Bootable USB Flash Drive – Latest September 2026
$12.99
RED HAT ENTERPRISE LINUX 5 SERVER RHF0382US-R1 for PC x86 AMD 64 INTEL 64 30 Day
$188.24
OPNsense pfSense 8-Core Atom C3758 2.2GHz 8GB DDR4 64GB SSD 8x NIC QAT AES VPN
$125.00
OPNsense Firewall VPN QAT 8-Core Atom C3758 2.20GHz 16GB DDR4 128GB SSD 8xNIC
$175.00
All New Ubuntu 26.04 LTS Linux Bootable USB Flash Drive
$15.95
1U Rackmount PC Intel Core i5-2520M 8GB RAM 500GB HDD Ubuntu Linux Server
$109.99
SQL Server 2022 Enterprise 96 Core License & DVD Unlimited CALs with CoA
$284.99
Sun Enterprise e450 400mhz cpu(x4), 4gb ram, 9gb HD w/spud most complete on ebay
$500.00