Can tokens be built on top of the LN?

Well I think you know the point of this article. Yes they can.
:P

So right now the only protocol for LN tokens being worked on and be coming out at the end of 2019 is RGB protocol.

The RGB protocol will be used by Spectrum.

This open-source token project, called Spectrum, includes contributions from investors at Fulgur Ventures and Poseidon Group, startups such as Bitrefill and Chainside, as well as support from crypto exchange giant such as Bitfinex.
Source: https://www.coindesk.com/startups-debut-first-protocol-for-issuing-tokens-via-bitcoins-lightning-network

RGB works in a very intersting offchain way. Smart contracts in fact can be done on RGB as well all offchain....
You can read how it works here:
https://steemit.com/busy/@sames/rgb-protocol-tokens-built-on-ln

RGB can be scaled further by statechains:
https://steemit.com/bitcoin/@sames/blind-statechains-with-eltoo

Another existing tokenization product built on Bitcoin albeit less bitcoinish than RGB is Counterparty. A once golden token standard...
They are planning on adding LN but IDK if it will be used by anything....
https://counterparty.io/docs/paymentchannels-lightning-faq/
https://counterparty.io/iconboxslider/lightning-network/

RGB sounds way more interesting and has the support of Bitcoin community more.

Keep mind there is also RSK, while not tokens on LN, it is a smart contract bitcoin sidechain:
https://busy.org/@sames/understanding-rsk-bitcoin-s-smart-contract-platform