Green’s Dictionary of Slang

(orig. US) any nameless small object, typically some form of gadget.

1911

L. Pound ‘A Second Word-List From Nebraska’ in DN III:vii 543: doobobus, doobobis, n. Vague designation used when exact word is not recalled, or is puposely avoided. ‘Hasn’t she a cute doobobus on her head?’ ‘Did you find the doonbobbis I wanted?’.