It is pronounced "sʊʒɛstjɔ̃".
You can also use these words depending on the context:
* Proposition (more formal, for a specific idea)
* Conseil (advice, a suggestion given to help someone)
* Idée (idea, a general suggestion)
Here are some examples:
* J'ai une suggestion. (I have a suggestion.)
* Voici une proposition pour améliorer le système. (Here is a proposition to improve the system.)
* Je te donne un conseil. (I give you some advice.)
* J'ai une idée. (I have an idea.)