なんでも相談会って英語でなんて言うの？

The words 'fair' and 'exhibition' are used for many projects where a group of people wish to introduce themselves or their businesses to the general public or, sometimes, just specially invited guests. For example, you could have a furniture fair, a toy fair, a job fair. Some of these may also be described: 'Toy exhibition,' 'Furniture exhibition' if there are physical goods to exhibit. With a job fair, there are no physical goods so this could not be described as an 'exhibition'. An 'Open day' is a word more suitable for organisations that wish to 'open their doors' so the public may see exactly what they do. Colleges and schools do this frequently. All of these events are designed to communicate with people and give advice and assistance about the various areas these organisation are engaged in.

A trade fair (or trade show) is an event where different businesses will come together and promote their products and services, and interested people can come and ask any questions they have about the company or its products and services.

I hope this helps :)

In some countries they have open markets where people have stall where they exhibit/show different talents.

A trade fair (trade show, trade exhibition, or expo) is an exhibition organized so that companies in a specific industry can showcase and demonstrate their latest products and services.

If you go to an event where you can find out / ask about a particular event that is happening
It is referred to as a 'trade show', 'trade fair' or 'trade exhibition' which all mean to show off a particular thing of interest to people and they can see about it and ask questions relating to it

An " Expo" is another, more modern way ,of saying:"Trade Fair".
These are well organised events where companies gather to show off their new
products and perhaps to give out /share information regarding new research and development on future products etc

An event where people can ask and consult about anything, is usually known as an "open day".