@chrillek is totally right. The complete example:
from pydt3 import DEVONthink3
dtp3 = DEVONthink3()
dest = dtp3.get_record_with_uuid('38DC985A-F8F6-4008-8DAE-24CBE9C68B2B')
new_record = dtp3.create_record_with({
'name': "TESTING OUTPUT",
'type': 'markdown',
'plain text': "blah blah blah"},
in_=dest
)
print(new_record.name)