What part of speech is underline MS. Sherry put the test on my desk

The part of the speech which is underlined is shown in the sentence below.

Sherry put the test on my desk.

The part of speech which is underlined is the preposition "on" which is used to link the noun "the test" with the possessive pronoun "my".

Prepositions are used to link nouns with other words within a sentence and some more examples include: to, at, after, but.