寥寥 rarely stands alone — it lives in fixed pairings: 寥寥无几 (liáoliáo wú jǐ, 'so few as to be barely countable'), 寥寥数语 (liáoliáo shù yǔ, 'a few brief words'), 寥寥可数 (liáoliáo kě shǔ, 'few enough to count'). Learn it through the chunks.
register
Literary register. In speech you'd say 很少 (hěn shǎo, 'very few') or 没几个 (méi jǐ ge, 'not many'). 寥寥 belongs to written Chinese — newspapers, essays, formal reports.
