Navmesh Enemy AI, Syntax issue?

First you should decide in which condition the user will be able to click on the enemy and make it go somewhere else. You may want the enemy to be affected by mouse click only when patrolling, only when chasing, only when attacking, or in the situations that can be combination of these. Once you decide, we can show you exactly in which part of the code you should be building your logic. In this case, all I can tell you is that you need to create some logic with booleans. For example, create a private boolean called "isClicked".

 if(!isClicked)
 Shooting();
 
 if(!isClicked)
 Chasing();
 
 if(!isClicked)
 Patrolling();

this will disable those functions / states if isClick boolean is true. So, when you should make it true ?

 GameObject[] markers;
      
      void Start()
      {
          markers = GameObject.FindGameObjectsWithTag("marker");
          //requires you to tag every marker as "marker"
      }
      
      void OnMouseDown() // Requires a collider on your character
      {
          isClicked = true;
          //if you use NavMesh
          GetComponent<NavMeshAgent>().destination = markers[Random.Range(0, markers.Length)].transform.position;
      }

Now the AI will behave as usual, and when it is clicked it will stop processing those Shoot/Patrol/Chase behaviours and go to the random selected marker position. Now you need to make the isClicked variable false again for AIs to behave as expected, and it is up to you to decide when to make the variable false again.

- You can use a coroutine, give a desired time.

 GameObject[] markers;
 public float waitTime;
 
      void Start()
      {
          markers = GameObject.FindGameObjectsWithTag("marker");
          //requires you to tag every marker as "marker"
      }
      
      void OnMouseDown() // Requires a collider on your character
      {
          isClicked = true;
          //if you use NavMesh
          GetComponent<NavMeshAgent>().destination = markers[Random.Range(0, markers.Length)].transform.position;
 
          StartCoroutine(WaitForSomeTime());
      }
 
      IEnumerator WaitForSomeTime()
      {
        yield return new WaitForSeconds(waitTime);
        isClicked = false;
      }

And now the AI return to its normal behaviour.

- You can check the distance to the marker :

 GameObject[] markers;
 public float distanceLimit;
 private bool canCheckDistance;
 private Vector3 posToCheck;
      
      void Start()
      {
          markers = GameObject.FindGameObjectsWithTag("marker");
          //requires you to tag every marker as "marker"
      }
      
      void OnMouseDown() // Requires a collider on your character
      {
          isClicked = true;
          
          //if you use NavMesh
          Vector3 markerPos = markers[Random.Range(0, markers.Length)].transform.position;
          GetComponent<NavMeshAgent>().destination =  markerPos;
          posToCheck = markerPos;
          canCheckDistance = true;
      }
 
      void Update()
      {
       if(canCheckDistance)
       {
        if(Vector3.Distance(transform.position, posToCheck) > distanceLimit - 0.5f) // 0.5f is the margin
        {
          //reached
          isClicked = false;
          canCheckDistance = false;
         
        }
       }
      }

You can also combine the 1st and the 2nd way together. You can first check the distance, and if reached, start a coroutine, wait for some time and then make isClicked false again in order to make the AI start behaving normaly.

PS. I actually did not inspect the AI code too much, so you may need to reset or tweak some patrol point variables in order to make the AI behave correctly after moving to a marker, because it may be away from its origin position once you make it go somewhere else with mouse click and this can cause some issues. So this is the logic that you can built, I hope I've helped :).