Ok.

Election law

http://www.slate.com/blogs/the_slatest/2016/06/30/looks_like_trump_s_campaign_has_already_violated_election_law.html

Super-Pac co-ordination

http://www.politicususa.com/2016/07/01/trumps-man-crime-spree-grows-felony-illegal-super-pac-coordination.html

Austrailian MP Tim Watts getting illegal fundraising emails from both Trump and his super PAC

Used corporate resources to pay for an election speech:

https://www.washingtonpost.com/news/the-fix/wp/2016/07/20/did-the-trump-campaign-violate-federal-law-by-using-a-trump-organization-speechwriter/

Business fraud/law

http://www.politico.com/story/2016/06/donald-trump-charities-fraud-laws-224510

Federal campaign law offering job for an endorsement

http://us.blastingnews.com/news/2016/04/donald-trump-campaign-in-serious-trouble-potentially-violated-federal-law-00860329.html

Copyright law during campaign

http://www.washingtontimes.com/news/2016/mar/24/trump-campaign-sued-for-copyright-infringement-by-/

Using a private jet which wasn't registered to fly:

https://www.nytimes.com/2016/04/20/nyregion/donald-trumps-jet-a-regular-on-the-campaign-trail-is-not-registered-to-fly.html

etc.

There's literally lists of stuff like this online, just put your post into google and you'll find more. Some of them are flimsy, however some are not.