Almost all of the ESP32 heap_caps_...() functions take a uint32_t caps argument.
In case you just want to have general information about the heap, use
MALLOC_CAP_DEFAULT
as an argument.
Most applications will rarely use any other value than MALLOC_CAP_DEFAULT. Other values which are used semi-frequently include:
MALLOC_CAP_SPIRAMMALLOC_CAP_INTERNAL(memory must not be located in SPI RAM)
For more details on how the memory of the ESP32 is organized, see the official documentation.