Reduplication

koaan, koankoaan, koaarn'koankoaan

Duples

You can repeat monosyllable A to get A'A, for some emphasis.

koankoaan (high)
ang'aang (red)
khuikhuy ((adj) opened. cf. khuy`khuy, meaning "to open")
khiuxkhiu (QQ; chewy)
lau-khokkhog, etc (Online Abbreviations)

Triplication

You can repeat a syllable A three times (A"A'A) to mean extremely A. Generally, the first syllable undergoes tone change to the rare rising tone (#6; see Tones of Taiwanese).

aarng'ang'aang (紅紅紅 x. aang - red etc)
jiirn'jinjiin (仁仁仁 x. jiin - firm & full)
koaarn'koankoaan (懸懸懸 x. koaan - tall etc)
loaan'loaxnloan (亂亂亂 x. loan - disorderly; chaotic)
kaao'kauxkau (厚厚厚 x. kau - thick etc)
zeerng'zexngzeng (靜靜靜 x. zeng quiet)
kiirm'kimkym (金金金 x. kym - golden))
khuiie'khuikhuy (開開開 x. khuy - wide open)
thoor'thothoo (塗塗塗 x. thoo - in shambles & completely lost)
kaao'kaokaux (夠夠夠 x. kaux - sufficient (cf. kaokaux))
siirn'sirnsixn (信信信 x. sixn - believing without doubt)
kof'kofkor (古古古 x. kor - ancient)
leerng'lefnglerng (冷冷冷 x. lerng - cold; cool)
seek'segsek (熟熟熟 x. sek - commonly seen; acquainted with)
took'togtok (獨獨獨 x. tok - alone)
siaap'siapsiab (澀澀澀 x. siab - bitter; astringent)
siip'sipsib (溼溼溼 x. sib - moist (cf. sipsib))

Zhamkhør

http://www.edutech.org.tw/Composition.htm
niaxnia (is this reduplication?)