Can I ask my employer to do another job if my doctor said I am unable to do my current job?

Your doctor, will need to be specific on what duties, you can or can not do.. depending on injury, hours can work, standing or sitting, weight to lift and so on.

You can then show doctor, note from doctor, that allows you to do, other or lighter duty. The work place is not required to give you other work. Many will, since it will often save them on WC costs.

That is normally a part of WC. The insurance company will try to find you another job. That way, they don't have to pay benefits.