public abstract class SkillBase
{
    // Common properties for all skills
}

public class WalkSkill : SkillBase
{
    // Some properties
}

public class RunSkill : SkillBase
{
    // Some properties
}

public abstract class EditSkillViewModel<T> : ViewModelBase where T : Skill
{
    public abstract T Skill { get; protected set; }
}

[EditViewModelFor(typeof(WalkSkill))] // Attribute telling that this viewmodel should be instantiated when we want to edit a WalkSkill object
public class EditWalkSkillViewModel : EditSkillViewModel<WalkSkill>
{
    public override WalkSkill Skill { get; protected set; }

    public EditWalkSkillViewModel(WalkSkill skill)
    {
        Skill = skill;
    }
}

[EditViewModelFor(typeof(RunSkill))] // Attribute telling that this viewmodel should be instantiated when we want to edit a RunSkill object
public class EditRunSkillViewModel : EditSkillViewModel<RunSkill>
{
    public override RunSkill Skill { get; protected set; }

    public EditRunSkillViewModel(RunSkill skill)
    {
        Skill = skill;
    }
}

public static ViewModelBase GetEditSkillViewModel(this Skill skill)
{
    var viewModelType = (from assembly in AppDomain.CurrentDomain.GetAssemblies()
                         from type in assembly.GetTypes()
                         where
                             type.IsDefined(typeof(EditViewModelForAttribute)) &&
                             type.GetCustomAttribute<EditViewModelForAttribute>().SkillType == skill.GetType()
                         select type).SingleOrDefault();

    return viewModelType == null ? null : (ViewModelBase)Activator.CreateInstance(viewModelType, skill);
}

var editViewModel = selectedSkill.GetEditSkillViewModel();