The BLE module used in the Solar powered IoT kit is CYBLE-022001-00. Please refer the CYBLE-022001-00 module datasheet for information related to pins.
You can find the kit schematic from the document "Solar-Powered Internet of Things (IoT) Device Kit User Guide". You can get it from the link below:
The jumper J2 present on the kit is free and you can use the pins present on it for your application. The J2 pins support I2C and UART interfaces. Please find the attachments. So you can connect I2C and UART based sensors to the kit.