How do I remove my personal data in the encrypted thumb drive? ... I have forgotten the password … unrecognised device
Crush it to small particles using a large hammer then buy your employer a new one (or ask them to deduct the replacement cost from your wages).
It is always a mistake to store personal data on the property of someone who you do not (or in future might not) wish to have access to your personal data.
A note on overwriting USB devices that use Flash memory.
Formatting any kind of storage device does not completely destroy data, it normally just recreates the filesystem structures without affecting much of the data contents.
For a hard disk, overwriting every data sector once with zeroes (or any character/octet) is sufficient to erase data. However this does not apply to flash-memory based devices such as typical USB memory sticks.
Flash memory devices use a concept known as wear-levelling, this means that some areas of storage will be rotated out of use and will not normally be accessible when using normal filesystem operations like writing a file. This makes erasing these devices more complicated. You need to make sure that any erasure tool you use is designed to work with devices that use wear-levelling.
A note on encrypted USB drives
I have an old Sandisk Cruzer device that uses the infamous U3 encryption system. When you first plug this in, all your computer sees is a small "CD-ROM" device that contains the U3 software and an autorun file. The encrypted data is in a non-visible "device" that the computer cannot see.
Only when you enter the password into the U3 software does the software make the encrypted device visible to the computer - which then assigns it a separate drive-letter (in the case of Windows) to that assigned to the pseudo-CD-ROM.
So if you don't enter the password, your computer cannot see the encrypted storage at all. Therefore no recovery/formatting/overwriting software can help.
U3 has some security weaknesses which allow you to bypass the password (Google will find this) but it is likely your device is better than U3.
A note on corporate USB drives.
Large serious companies that take security seriously are likely to purchase devices that can be centrally managed. Part of this is making provision for lost passwords by having a separate administrative password that can allow an administrator to regain full access to a device where the user's personal password has been lost.
This means that, just because you have forgotten the password, it doesn't mean a corporate administrator can't gain access to the data secured on the device.
A note on professionalism.
I would give some consideration to explaining the situation to your employer and working with them to resolve the issue to mutual satisfaction. This would be the "right" thing to do.
However, having stored personal data on a corporate resource, I sense that you are now looking for a solution that doesn't take corporate ethics and professionalism as a key point of reference.
A note about Rottweilers.
All in all, someone might regard it as a lucky blessing unfortunate minor disaster if their sister's Rottweiler chewed the device up and crushed the storage chips inside before they could rescue it. Make sure that doesn't happen to you.
If that happened to me, I'd offer to pay my employer the costs (hardware and administrative) to them caused by my foolish carelessness. Taking responsibility for their actions and paying for mistakes is something that adults are expected to do.
