How do I ignite the gas furnace when I cannot find the gas control knob?

Never saw a HW heater without some type of control.
https://cloudfront.zoro.com/product/full/Z0sK3xmcpEx_.JPG
Is this yours? Looks like a module plugs in the top. Note ON and OFF.
Honeywell says "Product is discontinuedNo alternate products can be found at this time".





https://www.grainger.com/product/RHEEM-DSI-Slow-Open-Natural-Gas-34VH45

You don't light it, you have a tech come out and troubleshoot your electronic igniter and flame sensor components.

https://cloudfront.zoro.com/product/full/Z0sK3xmcpEx_.JPG

See the on/off at the top... if indeed this is your unit. This is the one from Sears.

https://www.searspartsdirect.com/part-number/60-103901-01/0064/879.html?utm_source=bing&utm_medium=cse&utm_term=60-103901-01&sid=SPDxBING

https://s.sears.com/is/image/Sears/PD_0064_879_60-100394-03

http://i.ebayimg.com/images/i/181602146342-0-1/s-l1000.jpg

https://tse2.mm.bing.net/th?id=OIP.nLxfu9wPoamzAjL9L7nBbgEgDY&w=78&h=78&c=7&pid=1.1