import pandas as pd
import xml.etree.ElementTree as ET

xml1 = """<?xml version="1.0" encoding="ISO-8859-1"?>
            <pisteAuditProfilingQualif>
              ...
              <demande>
                ...
              </demande>
            </pisteAuditProfilingQualif>"""


xml2 = """<?xml version="1.0" encoding="ISO-8859-1"?>
            ...
              <demande>
                ...
                <REQ_TITLE_2>Sirrah!</REQ_TITLE_2>
                <REQ_NAME_2>George</REQ_NAME_2>
              </demande>
            </pisteAuditProfilingQualif>"""

df = pd.DataFrame({'a':[42, 54],'xml':[xml1, xml2]})

dfx = pd.DataFrame()
for x in df.xml:
    ex = ET.fromstring(x)
    ed = ex.find('demande')
    dfx = dfx.append(dict([(e.tag, e.text) for e in ed.iter()]), ignore_index=True)

print(df.join(dfx))

    a                                                xml  ... REQ_NAME_2 REQ_TITLE_2
0  42  <?xml version="1.0" encoding="ISO-8859-1"?>n ...  ...        NaN         NaN
1  54  <?xml version="1.0" encoding="ISO-8859-1"?>n ...  ...     George     Sirrah!

[2 rows x 12 columns]