Does type definition help assign restricted values?

In the below struct type:

type Employee struct {
	Name         string          `json:"name"`
	JobTitle     JobTitleType    `json:"jobtitle"`
}

member JobTitle should be ensured to have restricted(specific) values( of string type).

type JobTitleType string

const(
     GradeATitle JobTitleType = "Clerk"
     GradeBTitle JobTitleType = "Manager"
)

Does type definition(JobTitleType) help assign restricted values to member JobTitle?

No. You can assign any value to JobTitle:

e.JobTitle=JobTitleType("bogus")

The JobTitleType is based on string, so all string values can be converted to it.

You can use getter/setters to enforce runtime validation.

No, it will not restrict the values, any value that has type JobTitleType can be assigned to JobTitle. Currently, there is no enum type in Go. For restricting values you will probably need to write your own logic.

No, you should use it in the validation logic. For example, https://github.com/go-playground/validator has oneOf operator for validation.

Go don't have enum type, but you can do something like this

package main

import (
    "fmt"
)

var JobTitleTypes = newJobTitleTypeRegistry()

func newJobTitleTypeRegistry() *jobTitleTypeRegistry{
    return &jobTitleTypeRegistry{
        GradeATitle :  "Clerk",
        GradeBTitle : "Manager",
    }
}

type jobTitleTypeRegistrystruct {
    GradeATitle string
    GradeBTitle string
}

func main() {
    fmt.Println(JobTitleTypes.GradeATitle)
}