The MCP3008 talks to the Arduino via an SPI bus. Multiple devices can share 3 of those 4 signals, w/SS generally being a signal unique to each device. You still have the same question, as you’ll run out of SS pins. There’s also a limit on how many devices can be connected/share the same signal, like clock. But first you need to figure out whether the bus is daisy chained or not for multiple MCP3008’s.