Direct derivatives:
* loquacious (adj.): talkative
* eloquent (adj.): fluent and persuasive in speaking
* colloquial (adj.): characteristic of informal conversation
* soliloquy (n.): a speech delivered by a character alone on stage
Words with related meanings:
* locution (n.): a way of speaking
* interlocutor (n.): a person who takes part in a conversation
* loquacity (n.): the quality of being talkative
* eloquium (n.): the art of speaking well
* circumlocution (n.): the use of more words than necessary, especially to avoid saying something directly
Words with "loqu" in them, but not directly related to the root:
* locale (n.): a place
* locomotive (n.): a self-propelled vehicle
This is not an exhaustive list, but it gives you a good starting point. You can use a dictionary or online etymology resources to find more words with the "loqu" root.