Before listing my example, one remark regarding xml structures: when creating an xml structure, it is a better practice to use the 'class of the object' for the element's tag and store its 'attributes' like name and salary as xml attributes:
<employee name="Vineel Phatak" salary="520"/>
instead of:
<Vineel Phatak/>
This will make parsing a lot easier and gives more flexibility to extend the format.

My example

An example implementation for your questions:

import csv
from dataclasses import dataclass
import xml.etree.ElementTree as ET


@dataclass
class Employee:
    linenumber: int
    name: str
    salary: str
    manager_name: str
    subordinates: list


employees = {}  # a dictionary to map names to employees

# load employees
with open('company.csv') as csvfile:
    reader = csv.reader(csvfile)
    for linenumber, row in enumerate(reader):
        (name, salary, manager_name) = [value.strip() for value in row]
        employees[name] = Employee(linenumber, name, salary, manager_name, [])


# link employees to their subordinates
ceos = []
for employee in employees.values():
    if employee.manager_name == 'NOBODY':
        # store the ceos in a list to start building the xml from later
        ceos.append(employee)
    else:
        # look up the manager by it name
        manager = employees[employee.manager_name]
        manager.subordinates.append(employee)

# create xml
companyelement = ET.Element('company')

def add_employees_to_xml_element(xmlelement, employees):
    for employee in employees:
        employee_element = ET.Element("employee", {
            "name": employee.name,
            "salary": employee.salary
        })
        xmlelement.append(employee_element)
        add_employees_to_xml_element(employee_element, employee.subordinates)


add_employees_to_xml_element(companyelement, ceos)
ET.dump(companyelement)

# find the last entered ceo
def linenumber_key(ceo): return ceo.linenumber


last_entered_ceo = max(ceos, key=linenumber_key)
print(f"Last entered CEO: {last_entered_ceo.name}")

# find the last entered (in)direct subordinate of the last entered ceo
def find_last_entered_subordinate(employee, current_last=None):
    for subordinate in employee.subordinates:
        if not current_last:
            current_last = subordinate  # ensuring an initial value
        else:
            current_last = max([current_last, subordinate], key=linenumber_key)
        # recursive: travers the subordinate's subordinates
        current_last = find_last_entered_subordinate(subordinate, current_last)
    return current_last


last_employee = find_last_entered_subordinate(last_entered_ceo)
print(f"Last added subordinate of last CEO: {last_employee.name}")

I broke the excercise down in following parts:

1. Load Employees from a CSV file into a dictionary, to facilitate (and speed up) lookup of employees by name later on. I also store the line number of each employee to use for your later questions.
2. Link employees to their subordinates. Assuming that managers might be listed after their subordinates, this could not be combined in the first step. Every employee will have a list of its subordinates, CEOs are stored in a seperate 'root' list.
3. Create xml using element tree and a recursive function traversing the above created CEOs list.
4. Find the last entered CEO. We already have a list of CEOs, but because it is created from a dictionary (which does not ensure that elements are retrieved in the same order as they were added), I cannot just take the last element, but should find the CEO with the heighest linenumber.
5. Find the last entered (in)direct subordinate of the last entered ceo. Similar to above, this time I used a recursive function to retrieve this employee based on the linenumber.

resulting xml:

<company>
    <employee name="Vineel Phatak" salary="520">
        <employee name="Ajay Joshi" salary="250">
            <employee name="Abhishek Chauhan" salary="120">
                <employee name="Vijaya Mundada" salary="60"/>
            </employee>
        </employee>
        <employee name="Rajan Gawli" salary="700"/>
        <employee name="Sheila Rodrigues" salary="35"/>
    </employee>
    <employee name="Jayesh Godse" salary="500">
        <employee name="Shital Tuteja" salary="45"/>
        <employee name="Zeba Khan" salary="300">
            <employee name="Chaitali Sood" salary="100"/>
        </employee>
    </employee>
</company>