Will the mosque ask for my ID when I take my shahada?

It depends on the mosque. Islam doesn't require ID for the shahada to count, and many mosques will welcome you without it. Some do keep a register of new Muslims or issue a certificate, and then they may ask for your name and sometimes ID. You can ask what they record and why before you decide.

ID is not an Islamic requirement

Your shahada is valid when you sincerely say it, with or without paperwork. Any ID question is an administrative matter for the mosque, not a condition of faith. If you don't have ID with you, or would rather not show it, you can say so politely and see what they suggest.

Why some mosques ask

A certificate. To print your legal name correctly on a certificate of conversion.
A convert register. Some mosques keep a list so they can follow up with classes, support or a mentor.
Proof for later. A record helps a mosque confirm your Islam if you later marry, plan Hajj or need Muslim burial arrangements. See Do I need a certificate to prove I'm Muslim?
The mosque's own policy. For example, some check age or ask younger people to involve a parent.

What details might be recorded

Typically it is simple information: your full legal name, the name you'd like to use, date of birth, contact details, the date and place of the shahada, and the names of witnesses. A mosque doesn't need to know about your past, your family situation or your other beliefs.

If you've chosen a Muslim name, ask whether the certificate can show both names. Authorities for Hajj or marriage may compare the certificate with your passport. See Do I have to change my name after becoming Muslim?

Privacy: what you can ask

Your personal details are an amanah (trust). The Prophet ﷺ said that when a man tells something and then departs, it is a trust (Sunan Abi Dawud 4868). So it is reasonable to ask the mosque:

What do you record, and why?
Where is it stored, and who can see it?
Can I take my shahada without being added to a register?
Can I get a certificate later if I'd like one?

In many countries, data protection law also applies to organisations that keep personal information. You are entitled to ask politely about how yours is handled. For more on the Islamic view, see Does Islam protect the right to privacy?

If you are worried about family finding out

Say so at the start. Many imams are used to this and can keep things discreet, hold the certificate for you or delay any paperwork until you feel safe. Never give a false name, as a certificate that doesn't match your documents can cause problems later.

Key points

ID is not needed for the shahada to be valid.
Some mosques ask for a name or ID for a register or certificate.
Typical records are simple: name, date, contact details and witnesses.
You can ask what is stored and why; personal details are a trust (Sunan Abi Dawud 4868).
If privacy matters, say so before you begin.

Tip: When you book the appointment, ask: "Do I need to bring ID or give any personal details?" Then you'll know what to expect and can decide what you're comfortable sharing.