With the /check command in your membership bot you can see your user's summary:
ID number
Name
Email (if provided)
Status
Active plan (if any)
Resources access status
Payments history
Subscriptions history
Here's how it looks:
To use this command, you'll need the user ID number (this is the Telegram user ID actually).
Here's how you can get these IDs:
in payment/subscription notifications;
in the Dashboards / Export data (CSV) from the Telegram bot menu;
by forwarding a message from the user to @userinfobot in Telegram
in the SUCH web interface.
You can also ask the user to launch the @userinfobot in Telegram and it will reply with their ID number, which they can share with you.