These three words are known as scope adverbs in Chinese which are used as the constraint of the predicate element that follows, encompassing a sense of exclusiveness in meaning. All of them could be interpreted as “only”.
The use of Jìng (净) signifies that the speaker nurses a grievance against the situation, to be precise, Jìng (净) translates to “nothing but”.
tā de shū jià shàng jìng shì màn huà。
There’s nothing but comic books on his bookshelf.
tā jìng shuō xiē méi yòng de huà。
He said nothing but useless words.
The two adverbs zhǐ (只) and jǐn (仅) cloud be used interchangeably in most cases, nevertheless, jǐn (仅) is used more in formal contexts.
wǒ jǐn /zhǐ yòng le yí gè xiǎo shí jiù xiě wán le zuò yè.
It took me only one hour to finish the homework.
It is noteworthy that jǐn (仅) is often employed in its reduplicated form jǐn jǐn (仅仅), but unlike jǐn (仅), zhǐ (只) can’t be reduplicated as zhǐ zhǐ (只只) to serve as an adverb.
zhè běn shū wǒ jǐn jǐn kàn le yī xiǎo bù fèn
I only read a small part of this book.
Moreover, what directly follows jǐn (仅) could be a numeral- classifier construction, but a verb is necessary between the zhǐ (只) and the numeral- classifier construction in a sentence.
zhè zuò dà qiáo jǐn bàn nián jiù wán gōng le.
The bridge was completed in only half a year.
zhè zuò dà qiáo zhī yòng le bàn nián jiù wán gōng le
It only took half a year to complete the bridge.
Su X , He T . Chinese Lexical Semantics: 15th Workshop, CLSW 2014, Macao, China, June 9-12, 2014, Revised Selected Papers[J]. Lecture Notes in Computer Science, 2014.