Official presentation of the "Intel JTAG debugger" is .
The standard Intel debug port is the 60-pin XDP (eXtended Debug Port). It extends JTAG with additional signals. This port also has a lower pin count variant: the 31-pin XDP-SSA (Second Side Attach, designed to be on the other side of the board, where there are less components), and an even lower pin count variant: the 24-pin flex edge connector XDP-SFF-24. See  for a comparison among other debug ports (e.g., ARM, Nexus, ...). See  for guidelines regarding the physical layout of the XDP port. XDP pinout on page 23.
XDP includes an I²C line for SMB (System Management Bus).
XDP includes one or several observation ports (OBSFN_*, previously named "Breakpoint Monitor" BPM). Four are availables on the stardard 60-pin XDP, while only one is available on the 31-pin XDP-SSA.
Finding a dev. board with XDP access
The MinnowBoard features an Intel Atom Bayrail SoC processor ready to support Yocto Linux projects. See . An improved version can be bought there . The "High Speed Expansion Connector" gives access to some XDP lines such as the JTAG port and one observation port. There is even a breakout board (names "Lure" in this project) to route the signals to a more standard XDP connector, see .
Functionalities of Intel on-chip debug
The documentation of the Lauterbach debugger for Intel x86/x64  gives a list of many available functionalities. See  and  for details regarding traces.