As a sales representative, is it necessary to attend effective communication and negotiation skills courses and workshops?

I am not sure if it is necessary but, personally I found it to be hugely beneficial and it was easily able to implement to my daily activities and have since used it even out of the retail setting. I would also recommend body language training too as it helps you as the sales rep to get a read of a person even before you say hello.

yes off course that give him more information, tricks and any new update tools on his field

Not necessary, but it will definitely enhance your selling skills. 

Yes these are very important

Affirmative. People feel that its a norm to get annoyed with Sales reps because they speak a lot.

Therefore, Speaking the entire content with minimal words would make the conversation feel light and effective. Handling of irate and annoyed customers requires patience and smartness which can only be developed through workshops and communication trainings. 

You can't open a sale without communication skills and would never be able to close a sale without negotiation skills.                       Thank you

Sure he/she must attend to improve his /her skills

Yes, and yes. Simply, because life is a learning process, and you will learn many new skills everyday.

Happy Learning Dana Adel.

A sales representative should have these skills.. no matter if he is acquiring them before getting a job or after the job as a part of his/her training............... 

Companies are investing in their people to make them asset for the company and an effective field force is definitely a big asset of any company. 

Yes, sure. You have to attend such courses although I believe it's part of your personality. But you need the training to refurbish these interpersonal skills. You need to know the tactics used and identify people behavior.

It is essential for sales reps to communicate effectively with client and to be able to negotiate with customers as well, however if they possess these skills then it is not necessary for them to attend courses or seminars or workshops.  In the other hand, it is necessary for the company to train and refresh its sales reps every then and a while to keep their skills up to the edge in order to compete effectively.