401(k) reporting for S-Corp.
i would say elective employee deferrals do not show on page 1 of the 1120s rather they are part of salary and wages included on line 8 for non-officers and line 7 for officers. Say that a non-officer employee's gross is $15K and $2K is their elective deferral, I would show $15K on line 8 (the alternative to get the $15 salary deduction would be to put $13K on line 8 and $2K on line 17 but I believe this is incorrect). only the employer match, if any, would go on line 17.
The IRS recognizes that an S Corporation can sponsor a solo 401(k), also called an individual 401(k).
The caveat is that there must be no full-time common law employees and you and any other owner must have at least 2% of the outstanding company stock.
Despite its unique tax status, an S Corp is eligible to sponsor a regular 401(k) plan. if you go this route you should seek professional guidance because of the various rules that govern contributions, discrimination testing for highly compensated employees and other rules.
also an S-corp should be wary of classifying an employee as an independent contractor to avoid the 401(k) issue. if caught, the IRS could and has in the past disqualified 401(k) plans. it then taxes every participant on the value of their account.
you can read 1120 s instructions. look at the instructions for line 17
https://www.irs.gov/pub/irs-pdf/i1120s.pdf
here's a link discussing employer- Roths.
https://pocketsense.com/can-employer-contribute-employees-roth-ira-2878.html
and an IRS link discussing employee IRAs in general which should answer your questions concerning w-2s' and S-Corp reporting
https://www.irs.gov/retirement-plans/plan-sponsor/payroll-deduction-ira
for any type of employer-sponsored retirement plan, professional advice should be sought.
