Actually, in german businesses the usage of english (bussiness) terms has become quite common. Especially if these companies have one or more english speaking employees and/or operate largely outside of Germany.
So using "Gentle reminder" followed by a german sentence is totally fine, same as well-known abbreviations like "FYI" or "ASAP".
Most of the time this is used in subject-only e-mails as quick reminders.
Example:
"Gentle reminder: Deadline von Projekt xxxx ist am xx.xx.xxxx um xx:xx Uhr."
If you're not sure whether the company you're working with is multilingual or not, you should stick to the answers above, both IQV, simbabques and palloxs answers are totally fine.
Just make sure to be friendly and polite, as simbabque already stated.
EDIT: tried to be more constructive by adding another polite version including information the OP gave:
Sehr geehrte Frau xxx, sehr geehrter Herr xxx,
bezugnehmend auf meine E-Mail vom xx.xx.xxxx wollte ich noch einmal nachfragen, ob Sie mir die folgenden Informationen xxxxx zukommen lassen könnten:
- List item
- List item
- List item
Ich benötige diese Informationen, *** .
Für Rückfragen stehe ich selbstverständlich gerne zur Verfügung.
Mit freundlichen Grüßen,
xxx
At *** you could state reasons why you need this information. It helps to make them aware of the fact that you already asked once and really need this information, but without reminding them actively that they didn't answer yet, while also showing that you're willing to solve the issue asap and are happy to answer any remaining questions.