You suspect that a new ethernet card might be conflicting with another device. Which file should you check within the /proc tree to learn which IRQs are being used by which kernel drivers?

Answer: interrupts

Explanation:
The Linux/proc Directory is a Virtual Filesystem provided by linux kernel, /proc contains files and directories that let system administrators and programmers access system information.
The file/proc/interrupts file contains information on interrupts and IRQs. First Ethernet card device name is ethO, second Ethernet card device name is ethl…, to identify that dev will conflict or not, see the contains of file. Already ethO is appeared or not? Here is the output of /proc/interrupts CPUO 0:380893 XT-PIC timer 1:843 XT-PIC 18042 2:0 XT-PIC cascade 5:0 XT-PIC uhcijicd 8:1 XT-PIC rtc 11: 48 XT-PIC Intel 82801A A. ICH, ethO 14: 6086 XT-PIC ideO NMI:0 ERR:0 For a multi-processor machine, this _le may look slightly different:
CPU0CPU1 0:1366814704 0XT-PIC timer 1:128 340 IO-APICedge keyboard 2:0 0 XT-PIC cascade 8:01 IO-APICedge rtc 12: 5323 5793 IO-APICedge PS/2 Mouse 13:10 XT-PIC fpu 16:1118429415940594 IO-APICIevel Intel EtherExpress Pro 10/100 Ethernet 20: 8450043 11120093 IO-APICIevel megaraid 30:10432 10722 IO-APICIevel aic7xxx 31: 23 22 IO-APICIevel aic7xxx NMI:0 ERR:0 Appeared Number of CPU, Number of Ethernet card