Product type	Where to look
Headphones & Speakers	Earbuds print a small model code inside the charging case lid or on the stem. Headphones use the inside of the headband.
Musical Instruments & Pro Audio	The label is on the bottom or back panel near the power input.

Getting the official Sennheiser manual

Sennheiser publishes product documentation on sennheiser.com. Search there with the full model number from the label, then look for a documents, manuals or downloads section on the product page.

If your model isn't listed, try removing the last few characters, which usually only indicate color or region. For discontinued models, look for an archive or legacy products section, or contact Sennheiser support directly.