Not sure what TRONC is, but "salary" for the purposes of Skilled Worker visas is defined in
Immigration Rules SW14.1 & SW14.2.
SW 14.1. Salary only includes guaranteed basic gross pay (before income tax and including employee pension and national insurance contributions) and other guaranteed payments which are treated exactly the same as basic gross pay for tax, pension and national insurance purposes .
SW 14.2. Salary does not include other pay and benefits, such as any of the following:
(a) pay which cannot be guaranteed because the nature of the job means that hours fluctuate; or
(b) additional pay such as shift, overtime or bonus pay, (whether or not it is guaranteed); or
(c) employer pension and employer national insurance contributions; or
(d) any allowances, such as accommodation or cost of living allowances; or
(e) in-kind benefits, such as equity shares, health insurance, school or university fees, company cars or food; or
(f) one-off payments, such as ‘golden hellos’; or
(g) any payments relating to immigration costs, such as the fee or Immigration Health Charge; or
(h) payments to cover business expenses, including (but not limited to) travel to and from the applicant’s country of residence, equipment, clothing, travel or subsistence.
I am not sure that a zero-hour contract would meet the requirements for sponsoring somebody on a Skilled Worker visa.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.