Hi!
Is there any possibility to invite a user to answer a question? Like here, in Quora:
Yes, use the invite button on the topic.
You must be TL2 to send invites however.
Agree with Jeff, right now @Agnieszka_Jaskiewicz you have TL1 here on discourse.
When you get the TL2, you will see the “invite button” like:

Some off-topic points:
Regards!
Thanks! What do you mean with TL2? What are the next steps when a user gets a request to answer a question? Does he get an email or what?
Search “trust level howto”. Find Understanding user statuses, roles, and permissions
我们的用户默认拥有 TL2 权限。我希望将“邀请回答”选项仅保留给管理员,因为我担心用户之间会互相发送垃圾信息。我们该如何从 TL3 开始启用此选项?