If you are interested in someone there are a few things you should do.
First introduce yourself to said person
Then chat with them. If they are also interested they will be receptive of this.
If during step one or two they have not brought up the subject. Ask them if they are free to meet up. At that point they generally will let you know if they are available.
If you have gotten this far you should have determined that by agreeing to go out they are not in a relationship.
This is where it gets tricky, if you have not yet established a relationship you are both still able to talk to whoever you want. So by looking into his life to find out who he “talks” to is borderline creepy stalker behavior.
Instead after a few dates based on how they go you will get to a point naturally that you will want to let him know if you are happy with how things are going. You can inquire if he feels the same and if he is ready to give this a chance. You can confirm if he is at a point that he is no longer dating anyone else.
Then after both parties have given understanding of what your status is you can if needed ask him if he is talking to someone else.
The only way to get answers about what someone is thinking or doing is to ask them directly. Any other method is probably going to give you bad answers or classify you as a crazy stalker. It's not a good way to start a relationship and not a good way to keep one.