On-scalp digital printing of custom-designed, temporary-tattoo-like sensors represents a groundbreaking advancement in noninvasive brain-monitoring technologies, advancing the fields of neuroscience, clinical diagnostics, and brain-computer interfaces (BCIs). Traditional electroencephalography (EEG) systems involve time-consuming manual electrode placement, conductive liquid gels, and cumbersome cables, which are prone to signal degradation and discomfort during prolonged use. Our approach overcomes these limitations by combining material innovations with non-contact, on-body digital printing techniques to fabricate e-tattoos that are self-drying, ultrathin, and compatible with hairy scalps. These skin-conformal EEG e-tattoo sensors enable comfortable, long-term, high-quality brain activity monitoring without the discomfort associated with traditional EEG systems. Using individual 3D head scans, custom sensor layout design, and a 5-axis microjet printing robot, we have created EEG e-tattoos with precise, tailored placement over the entire scalp. The inks for electrodes and interconnects have slightly different compositions to achieve low skin contact impedance and high bulk conductivity, respectively. After printing and self-drying, the inks form conductive, stretchable, and breathable thin films that ensure high signal fidelity, even over extended periods. This technology paves the way for non-invasive, high-performance, and user-friendly brain monitoring that will enhance both patient care and the understanding of the human brain. The broader significance of this technology lies in its potential applications beyond traditional EEG use. On-scalp printed ultrathin e-tattoos could play a pivotal role in developing BCIs for various industries, including prosthetics, virtual reality (VR), and human-robot teaming. This work also opens the possibility of on-body digital manufacture of other types of e-tattoo devices in areas beyond the head, leading to large-area, skin-covered yet deformable and breathable functional e-tattoos.